Greater accuracy in placement, spacing, sizing etc and less abrupt rounding is of interest to me as well. I enter numeric values quite a bit throughout both Finale and Sibelius currently.
One of the largely unknown features of Finale which I really like is the ability to enter measurements in different units on the fly by using a letter code at the end of the numeric entry in any entry field throughout the application.
So, for instance, if you are viewing in inches but want to enter a value in spaces, you can type “1.25s” and the program understands that as 1.25 spaces. or if you want 1.25 points, enter “1.25p” or “1.25i” for inches. I also employ Finale’s EVPU measurement because it offers a way to enter whole numbers which are easy to remember for very small measurements; “3e” (for EVPUS).
Something like that would be very useful, if not completely proprietary. (Note that because this feature was understood by so few, MakeMusic went on to add drop down menus to change unit of measurement in some, but not all individual dialogs.) But for someone familiar with the shortcut, it is very powerful.
The “Staff Unit” type mentioned by you, Paul, sounds very useful.