Does your motherboard support crossfire? I have an 8800GT still and I can SLI them with a 2nd, but my motherboard only supports crossfire and not nvidia's SLI
That's a tough call.. crossfire and SLI have gotten a lot better recently with their performance but it still usually requires specific support in the driver (though I've read you can make your own profiles), so one thing would be to check if the games you play the most work well with crossfire.. it would suck if you got it and found out your #1 game got zero benefit.
You'd definitely see some benefit for the SSD as well, everyone that has one will tell you it's night and day, Anandtech says it's the one upgrade you can do that has the most impact on how fast you perceive your computer running. Just be careful with the Kingston ones make sure you do the full research on the drive, I think there's ones that are reasonably fast for the price, and ones that are cheaper but really slow.