I would also like to add that I agree with the notion that upgrade scripts would most likely be useless. The current version required so many changes to work for us that anyone who uses it seriously would need to upgrade manualy anyways.
I'd also say that it should be an upgrade to the current package, not a new package. Nothing in your description indicates that the old one would ever need to be used instead of the new one. Only that existing installations may not be able to move over right away.
I don't think I would upgrade my existing sites, since I've already hacked in fixes for all the bugs they had and customized them for the client. Plus, that would require a budget from them :) But if you release this version, I would definitely build on it for any new production sites I use it in.
-Jacob
