I'm coming to this debate rather late, but it seems kind of clear to me:

- Brainstorm is for ideas and enhancements
- Bugzilla for bugs

As it is anticipated that there will be a flood of new users, you want something that is "as simple as possible but not simpler".

There is nothing stopping experienced users from entering those super-specific enhancement requests direct into Bugzilla.
For things that are incorrectly placed in Brainstorm, the moderators could open the bug and add the appropriate user-details.
Over time, the new people get used to Bugzilla and the difference between the two, *without* overloading Developers.
Yes, this puts extra work on people to move those ultra specific enhancement requests from Brainstorm to Bugzilla (or to the appropriate upstream project), but I see this as a better method because the user education happens only "as needed", rather than attempting to boil the ocean and educate people about subtle differences and getting more mainstream humans to fill in bugzilla.