My advice is to roll with the GT 520 until you can afford a better PSU, and then to upgrade that first.
I can find no reviews for that unit (not a good sign!) and plenty of people having issues that went away when that unit was replaced.
I wouldn't increase the load you're putting on it one bit.
Something in the $50-70 range from Antec, Corsair, Seasonic or any of the other usual suspects (the stickies in this section have a nice list) will let you use all sorts of fun GPUs.
As it stands you have the right GPU for that PSU in my opinion.
I'm sure this is exactly what you don't want to hear, but I would far rather annoy you by saying it than see you buy a shiny new GPU and have the PSU fail and kill it, along with everything else plugged into your PSU!
Lastly, welcome to overclockers.com!