I think of shrink-wrap as a 'bells and whistles' version of a derived part. Woudl this be fair?
Well today I thought I had the ideal opportunity to use one. I have to bring a large sub-assembly into an assembly I am designing. The sub-assembly has been pack and go-ed to me from elsewhere. I thought it would be good practice to substitute a shrink-wrap version of the S/A. To try to ensure that it looked the same as the S/A, I opted for the 'solid body, keep seams between planar faces' option.
But it came out looking rubbish. Too many bits were missing. I attempted to edit it and turn on visibility of the missing parts, but it didn't work. File size was 9600 KB.
So I decided to try an 'old school' derived part. This did eventually work, but file size was a whopping 42708 KB!
I realise the file size given of an assembly isn't the 'real' size, but I find it hard to believe that this derived file is smaller than the file it's meant to be replacing.
So although it looks like shrinkwrap parts are smaller files than 'ordinary' derived parts, that's no good if they don't look identical to the original assembly.
Shrinkwrap is in fact a type of derived part, so you are correct there.
There are several settings that affect the result you get from the shrinkwrapping.
Remove Geometry by Visibility: Allows removal of parts that are obscured from view (such as internal parts). If the percentage of this is above 0%, it will start hiding parts that are only partially obscured. For your case, I would recommend leaving it turned on, with a percentage of 0. This should only remove parts that are completely internal.
Remove Parts by Size: The higher this is turned up, the larger the parts it will automatically remove. In the case of what you're wanting to do, I think it would need to be unchecked completely.
Hole Patching: Generally, the more you want the shrinkwrap to look like the original, the less patching you want, since it will close off openings that were present in the assembly. Therefore, you should probably set it to None.
I will point out that part of the memory saving ability of a shrinkwrapped part comes from omitting unnecessary detail. The more you insist that it look identical to the original (showing every part, no holes patched, etc), the less good it is going to do you on saving memory.
As someone who is still stuck on 32 bit WinXP, I will assure you that shrinkwrapping, while not always perfect, does help. I have been in many situations, especially with reusing imported 3D AutoCAD data, where I would literally have been unable to complete the work without using shrinkwrapping.
I would encourage you to go ahead and set up a shrinkwrap level of detail, then look at the difference between Inventor's memory usage between the master and shrinkwrap LOD's. You might be surprised how much of a difference it makes.