I'll throw my 2 cents at you as well...
Accelerated 2k to stock 3k, will not light your pants on fire by any means.
If you add video and acceleration to a 3k, buy a new set of pants. The difference will burn them right off. Z3 and the faster bus give huge performance gains over a similar built 2k. I ran similar systems (3k with 40mhz 040 and retina z3 and 2k 040@40mhz and retina z2) side by side and the 2k was way slower.
The other item is a taste thing, many believe the 3k was the best built Amiga. Certainly a 3000+ would have filled everyone's dreams of what the 3k should have been. But if you think the 3k would be fun and can pick it up on the cheap. It might be fun to play with, go for it.
The battery issue on a 3k isn't always an issue. I replaced batteries on 3 different 3k's all with major leakage. I cleaned the acid and mounted a new battery and they worked great. So if they boot with a leaking battery I wouldn't run away from it.