Splitting up this post:
https://forums.autodesk.com/t5/3ds-max-ideas/improvements-to-parameters-in-the-ui/idc-p/7429821#M238...
The old spinners are tiny - 11x7px. Just too small to be comfortable, since each arrow should be clickable separately.

But even if the input field would be bigger, the arrows would still be comparatively small.
Possible solution:
The whole input field could be the spinner! In that case, the spinner arrows sould better be to the left and right of the input field.
Like in Blender.
I don't need range sliders, like e.g. Softimage. An endless spinner does the same thing, uses less space, and it doesn't have to worry about it's range.
(It's a nice feature of Max that the cursor wraps around the screen borders when 'spinning', btw.)
To scrub the parameter: LMB-drag left/right anywhere on the parameter (instead of up/down on those tiny old spinners).
Accelerate spinning: CTRL-LMB-scrub
Decelerate spinning: ALT-LMB-scrub
To place the cursor into the input field to edit: LMB-release
In Max you can directly select text in the input field. This should still be possible, for example with MMB, or SHIFT-LMB etc..
Mockup of horizontal spinners:

Thanks!