I would first upgrade the PSU as mentioned. I dont trust stock psu because they go cheaper alot of times and I learned my lesson not to go cheap on a PSU, but thats not saying you have to spend alot.. I found a Corsair 750 watt enthusiast for $95 new. Seasonic makes PSU for Corsair so Seasonic are good. A psu is going to lose wattage over time, up to 30% if your juicing it all the time over a few years, so I suggest going with more than you need.
If you are playing SWTOR, like any mmo, you do not need a very good card. I played SWTOR and WoW both in ultra with two Geforce 9800 GTX+ cards and pretty much had no problems at all.
That is the equivalent from what I have seen of 1 Geforce 550Ti which are selling for as cheap as $120 after rebate at a local Fry's if you want to get going fast.
You have Guild Wars 2 coming out at end of the year and do not know the specs, but probably will not be much different.
I just got a Geforce GTX 560 which is about $175 after rebate, but is a major jump in performance from the 550Ti. I saw framerate go up about 25% in SWTOR, and my computer buddies run all their games on ultra with a GTX 560 with no problems. Personally, I am thinking the GTX 560 is a bit of overkill, for mmos even, but there are more knowledgable people than me