I'd honestly say... no, it's not worth your money, for two basic reasons:
1. a GTX 275 is a GTX 260 with 24 more CUDA cores and almost 40W more of TDP.
2. current 400 series from NVIDIA is even better and at a similar price point.
If you're very tight on budget and you can pass on DirectX 11, go for a GTX 260, it will be cheaper, quieter, 216 cores are more than enough for current games (at moderate-to-high quality settings) and it won't be stopped by your current CPU (I had a Phenom II X4 905e @ 2.5GHz / 65W, and it didn't really go slow).
So, essentially... that. If you're very tight, GTX 260 (it's my recommendation, at least). If you can grab a couple more of dollars/euros here and there... a GTX 460 is a good card for you.
Hope that helps
EDIT: Didn't fully read your comment, sorry... go with the GTX 275. Worth it? For sure! going from 128 to 240 cores IS a big difference