I wouldn't get your hopes up too much, looking at the GTX500 series. Sometimes, previous-gen models will stick around in stocks and keep dropping in price, but often it's not the case. The GTX570 and GTX580 have dropped a little since GTX600 launch, but they're still nowhere near where they should be priced relative to the GTX660. If you want a GTX670, I'd just grab one as soon as you see a good price on it. Best reason to wait for GTX700 is if you want something faster.
Also, I'd be totally shocked if Nvidia gets the 700 cards out before August this year. I think we're 6-8 months minimum away from 700 series launch. Remember, it's only been a couple months since they got their full 6xx series out the door.