How much room do you currently use system wide? And do you have any data that you consider important/irreplaceable?
You could raid the two 500gb drives and get a 1-3tb drive as a backup/storage drive. I think this would be the best performance+recovery/$ option.
See if you can score a deal this weekend and look for 2 1tb drives and a 2tb drive for r0 + backup drive. W/o a deal this would probably be ~$200.