How do I create AEC Objects with visible layers that do not plot?
If you are going to throw all of the non-plotting components on one layer anyway, why not create one layer for that purpose (A-Wall-Nplt-N?), and leave Defpoints alone? I try to avoid using Defpoints for anything other than for what AutoCAD (Architecture) uses it. That also allows for the possibility of changing the plot status of that layer should you have an occasion where you want to plot those items, such as for checking purposes.
A non-plotting layer is probably the better approach. You can set up a plot style that does not plot (set it to 0 percent screening; see Invisible Ink in the Aec Standard.stb plot style file for an example), but if I recall correctly, that is not truly non-plotting - it just uses the background color. So if your non-plotting component is on top of something that plots, the "invisible ink" component will overwrite the plotting component with "white" - similar to a wipeout.
I am not in front of a computer right now, so this will not be an exhaustive response.
Changes made to styles or drawing-default display settings will only affect that drawing, unless you copy them to other drawings.
In order for each Wall Style to have its own display settings for the same components, you either have to create a style-level override for each style -or- you have to set component display to be by material, and then assign Material Definitions to each component that have style-level overrides of their own to have unique display settings. The out-of-the-box Wall Styles use the latter method. This makes it easier to get the same settings on the same component type (for example, brick) across all of your Wall Styles. It also makes it easier to make a change to all of them, as you only have to edit the Material Definition, not each Wall Style.
Anything you can do in the Wall Style display overrides for a component you can do with a Material Definition. You are just moving the place where the settings are stored from each Wall Style to a Material Definition.
I looked at the Siding, Sheathing, 2X6 Studs, and GWB Material Definitions that you set up. You had a style-level override in each for the General Medium Detail Display Representation for Material Definitions, which is the active Display Representation on the Model tab of your file. That is good if you want to be able to have unique settings for each Material Definition. (If you go this route, you may need to add overrides for other Display Representations if you use them in other View Directions or other Display Configurations.)
In those overrides, you changed the settings for the Hatching of the Plan Hatch component, which are reflected in the drawing. But the settings on the Layer/Color/Linetype tab are all the same, so they will display the same. All but two of the components on that tab are set to Layer 0 with ByBlock attributes, so they will show with the attributes of the parent Wall. (Sectioned Boundary and Sectioned Body, which are not on display on the Model tab of your drawing, are similar, but have explicit assignments for Color.)
If you want the components to have different colors, lineweights, or other attributes from the parent Wall, then you need to make those assignments in the Material Definition, on the Layer/Color/Linetype tab.
I attached the modified file.
Your understanding of By Material is correct. Material Definitions provide a way to set component display settings - including hatches and render materials - for a given Wall component (such as Brick) in one place and apply them to multiple Wall Styles. If you later decide to change your standard, or if a specific project requires a change (eg, yellow brick instead of red brick), making the change to the Material Definition for that project will make the change to the components of all Wall Styles in that file that use that Material Definition.
How you choose to show existing vs new is up to you, based on your typical workflows. My firm does mostly commercial and institutional projects. Our floor plans are typically at 1/8" = 1'-0" and we only show the Shrink Wrap component, not the individual components, as at that scale the lineweight of the component lines is often wider than the actual component width. We do set our Wall Styles up with all of the components and have a Display Representation that will show them and any hatches if we do enlarged plan details from the "live" model. We handle new/existing/demo by the settings on the layer of the parent Wall object. (Shrink Wrap is not by material, but on Layer 0 with ByBlock properties and the parent Wall's properties are ByLayer.) We have generic existing-to-remain and demolition Wall Styles that are set up with variable-width single-component for modeling existing conditions where we do not know the composition of the Wall (but have a reasonably close understanding of the overall width of the Wall). If we are renovating an area where we were the original design architects and did the original drawings with ACA Walls, we will just change the layer to an existing layer for items to remain or a demolition layer for items to be removed. Since we are not showing components, that works. If you want to have multi-component existing and demolition Walls that parallel your new Walls but omit hatches then setting up a Material Definition that has the Plan Hatch component turned off would be a way to achieve that. If the Plan Linework component can have the same settings for all components, you could have just one Existing Material Definition that would work for all components. In other words, you would not need a whole new set of Material Definitions for existing to remain Walls, one for each new Material Definition.
ByLayer vs ByBlock: Which to use depends on where you want to control the display of things, and whether you are assigning explicit layers in the display settings. For components that are being placed on Layer 0 (so they inherit the layer of the parent Wall object), I generally prefer to use ByBlock for attributes (Color, Linetype, Lineweight, etc.) that are not being given a specific value. 99.999% of the time, the parent Wall object will have its properties set to ByLayer, in which case ByBlock or ByLayer will have the same result: changing the setting on the layer (or changing the layer to one with different settings) will be reflected in the Wall. But in the 0.001% of cases where I want to do something unique to a very small number of Walls without creating a new layer for them, the ByBlock setting allows me to change the properties of the parent Wall and have the component show that. If you want to control things at the layer level and prefer to create a new layer if you need to change the properties, then use ByLayer. This blog article has an attempt I made to illustrate the differences between assigning ByBlock and ByLayer to nested objects in a block definition. The example uses Color, but it applies to the other properties also. Display settings on components of AEC objects, like Walls, behave the same way. There are three levels to the Display System. Drawing Default settings apply to all objects that do not have an override. Style-level Overrides allow you to have settings that only apply to objects of that style or definition. These can be useful if you need to show the same component in a different way in different styles. But that also makes it difficult to make changes to similar components in multiple styles. The By Material option was eventually added as a way to be able to vary the settings of each component while having one place to make the settings (and any changes) for all similar components across all styles. Object-level overrides are the final level, in which you can have unique display settings on individual objects. These should be used sparingly, if at all, because you have to edit each object if further changes need to be made.
Unfortunately, overrides are an all-or-nothing thing. If you set an override, it applies to all settings in that Display Representation. You cannot just override the settings on one component and have the rest follow the Drawing Default settings, picking up any future changes made there.
As for the dashed line issue when moving the Existing Wall to the demolition layer, in your four "Invisible" Material Definitions, I changed the Linetype of the Plan Linework component from ByLayer to ByBlock, so that it now inherits the linetype of the Parent Wall. That remains a continuous line when on the existing Wall layer, but changes to a dashed line when on the demolition Wall layer.
Apologies for the unclear terminology.
When I said parent Wall, I was referring to the Wall object itself. The use of "parent" was an attempt to describe the relationship between the Wall object and its "children" components.
When using ByLayer for a particular attribute of a Wall component, that component will pick up the property value of the layer assigned to that component, except for Layer 0, in which case it will pick up the property value of the layer of the "parent object" - the Wall.
When using ByBlock for a particular attribute of a Wall component, that component will pick up the property value of the "parent object" - the Wall. If the Wall property is set to ByLayer, then the component will pick up the property value of the Wall's layer. If the Wall property is set explicitly, then the component will pick up the explicit property value.
