The Phenom X4 915 is Socket AM3, the 3+ board won't provide any noticable advantage over an AM3 board (which are real cheap now) BUT... you'll have to upgrade ram to DDR3 also (not too expensive). If you do upgrade to AM3+, you'll be poised for a Piledriver upgrade when it's released. You'll get a little more performance out of the processor but I doubt you'll see a major change in frame rates (I could be wrong).
Yep, and an upgrade (either AM3 or AM3+ and the corresponding ram upgrade) will give you more performance out of the CPU you currently have which is AM3. I don't know that it'll be a huge leap in performance though.
But I am confused since the AM3 has 941 pins and the AM2 940 pins... how does that work? Is the processor the 9150e (AM2+)? Then upgrading would involve mobo, ram and CPU.