Yeah, portability is a major factor for me. Another great unlooked feature of the AC-30 as a halfstack would be that the 4x12 cab has a magical little thing called 'wheels'.
After lugging around my old 2x12 Line 6 Flextone III, I decided that carrying 60 pounds around with me isn't much fun, especially for gigging... Of course, a 4x12 is going to be heavier, but wheels are great. Also, no need to mic a 4x12 cab in smaller venues.
Another benefit I found was that in most of the local shows we hit, the headlining band brought their Cab and everyone else just plugged their head into the headlining band's cab. Depends on how picky you are about your tone though, and if you're touring multiple states, but I thought that was a decent benefit
No one happens to know what tubes the AC-30's run standardly do they? Thanks for everyone's comments already, they've been a big help. Keep 'em coming!