Upgrading a 2010 Macbook pro
I used to work with a 2009 MBP 13" with C2D 2.53Ghz, 8GB ram and 256GB SSD, it worked like a charm with development (Qt, XCode), VM (VirtualBox), image edition (lightroom).

I changed it because the screen was too small but that shouldn't be an issue for you since you're running on a 17". So if you change both, you can hope at least 2 more years.

I would go for the SSD which is awesome : your HDD should reach around 100MB/s in RW whereas the SSD can go up to 375MB/s in SATA2 which is very nice. You'll get more speed in loading softwares, and swapping will be faster in order to compensate the eventual lack of RAM.