Apple is always mixing things up with their graphics card selections. Now, I prefer the Nvidia cards used in the MacBook Pros now rather than the ATI card they used to have, but I would prefer the ability to choose one or the other like the Mac Pro. Of course, Apple wouldn't give you too many options, but having to choose between two cards is better than being set with just one. I would like to see an option for Nvidia cards in the next update.
Rumors of the hard drive changes don't bother me much. Graphics and clock speeds are the only things in this update that may catch my eye.
Anyway, I'm hoping for a Mini update. That would give me more reason to go get one... 
The only thing Apple needs to worry about updating is their display line. Those things need to be revamped. And price-cuts would be very nice. And while I add to this growing list of things Apple should include here, I think they should reintroduce an external iSight camera of some sort for use with a Mac Mini or Pro.
-BMF