Hey Jim, very good points, much the same as in my thread in the beta forums concerning profile field mapping... check there. Leshrac has some scripts to move profile fields around, and while they look good, standardization is still something we should look at. An "auto-install/ update" mechanism is being developed by borg that all major modifications will be adapted to and standardization can only help here...
There is a thread in chit chat from a while back where Navaho discusses developers "signing up" for profile fields, then everyone knowing that those fields are reserved for use by that particular modification. Some might argue that it'll leave some users with 50 fields in their profile when they only wanted to install one modification, but it so happens to use field # 50. I really don't think this will present a problem, or cause any additional overhead.
Having said that, you might consider using a higher # for your profile field, to prevent any conflicts, but it's up to you. You might wanna present your POV in the thread in the beta forum.