I would suggest putting slicks on your current bike and tring that out. $500 doesnt do much towards buying a new road bike. If you start saving now, you should be able to get a roadie in a few months. If you want brand new from a shop, $1500 gives you a few options. yes you can get one for less but you're sacrificing quality and performance.
on a seperate note, if your hardrock needs an overhaul, why not try it yourself. there are numerous how to videos on utube, and search out sheldon brown. It would be great practice before you get that shiney new rocket. its cheaper and more rewarding to self wrench your ride. if you get stuck then bring it in, they love that.