Perhaps. I find that the extra memory benefits me when I am doing more than one thing at once. Like a video encode and a couple other things in the background, then when I try to browse the web it swaps and crawls with 512. Faster with a gig.
As far as price, you can get a gig for $110-$120 (see link I posted above). 512 is prolly half that much. So it's a difference of $50-$60, which may or may not be worth it. Depends on what you are doing with it, again. For games only, maybe not.