UA has a lot of stuff that looks interesting but also could be terribly broken. Definitely one of the parts of 3e that needs a lot of DM curation.
Gestalts are probably one of the biggest examples of this. The book warns that it's a powerful option which I read as "pretty damn broken". But I think limited gestalts might help to recapture some of the feel of AD&D multiclassing. In particular, I'd mostly limit it to the most iconic class combinations of the past. Also, I think this could be the real niche for the half-elf, since they had the best multiclassing options. I'd definitely have to tone something down about it first though.
Recharge magic looks like an interesting option on the surface, but I suspect it powers up casters. Also it seems like it would increase bookkeeping. So I wouldn't use it.
No opinion on spontaneous divine casting.