The price drops wont be much at the beginning and with the 600 series not being due out for about 3 more months the random price drops and newegg combo deals between now and then will be more significant than the small amount they will drop on launch date, and if supply on the 600 series is low like it was for the 400 series prices might actually go up a bit.
Flagship cards (or close to flagship, like 570) generally don't see price drops. I used to have a 8800 Ultra some 4 years ago and I was always waiting for 9000 or 200 to make its price drop, so I could go SLI withouth having spend some extra $600. It never happened and I had to buy a new card. That's the way it is, always.
Just get a 570 now or a 670 when it comes out. The only perfect time to buy a graphic card is when price makes a $20 drop or a new card comes out. 570 already cost ~350 for a good card so it is a small difference.