The difficulty level is increasing significantly right now. You may or may not see a payoff on your card purchases unless BTC prices rise again. If you're really interested though, fast AMD cards are the way to go right now with the 7970 leading the pack.

I'll give you the same advice I give everyone else: if you're looking for an excuse to upgrade your gaming rig and picking up a few BTC over the next month or two is enough to push it into 'buy' territory for you, it's OK. If you're looking to get rich quick, you're already too late.