It isn't any better to buy a new card more often. You simply lose less money more frequently (and ends up adding to more of a loss actually) rather than lose a lot every other year. The only thing that makes any real sense is to admit defeat and embrace the console revolution. Seems like the GPU industry is trying to "encourage" PC gamers to move toward consoles in order for their profitability to really increase. They do this by over charging for mid range products and discouraging purchases of GPU's by releasing the same card for $100.00 less like they did with the 670. In another few months they will hammer us again with the 685. They want us to grow tired if this and embrace the new console revolution coming with the new console generation.
They create a problem for us, and then offer us the solution in the form of a console.
Don't be ridiculous. Not only you lose less money if you upgrade and sell frequently, but you also get the perk of always using the best technology has to offer. If you want to keep your 570s, go ahead. One 670 would perform just as well (and better in VRAM limited scenarios) and would probably net $100 in your pocket at the end of the year just in power savings. You would actually EARN money from switching to a 670 right now until the end of the year.