I've mulled this over too. (See my sig for my MBP).
For me, the main, and most notable advantage would be the ability to utilize 4GB RAM or more. I run Paralles, and VMWare daily (and even VirtualBox on occasion) and would love to throw more RAM out there.
I doubt there would be significant performance gains for you, but, as mentioned, the video would be snappier and you would have a higher frame buffer if you opted for 512MB VRAM (frankly I wish they would throw a 1GB sku in the mix).
I did as suggested too.. I updated the RAM and the HDD to breathe new life into my MBP and that does help a bunch.