Yes, Phenom II will be compatible with AM2+. However, that is assuming your motherboard manufacturer will create updates for all their AM2+ BIOSes.... which isn't a given.
Phenom II will be a big jump, however, so I'd agree with the wait sentiment, if cost is not too much of a factor. It could be that you may end up having to shell out extra for a new motherboard.
But, just FYI, the Phenom 9950 outperforms all the AMD duals in games. It does have better clock for clock performance than Athlon, even ignoring the extra two cores. The only real tricky thing about the 9950 in particular, is that some models are 140W TDP, and some are 125W TDP. The latter one is probably preferred.
If you are into overclocking, it won't be pushed very high unless you have a 750 southbridge on your motherboard. Otherwise, with very good air cooling it can probably go to 3.4/3.5 Ghz, and with water just a little bit higher.