keep on buying ps3 games. The new consoles won't come out until christmas next year, but that doesn't mean that the current gen will be outdated. For all of us ps3 users, Sony announced that they would support the ps3 until 2016. That's perfectly fine with me because I don't want to waste the money to buy a new console when I could just get other games for the ps3. As for thinking the games are a waste, if you buy all the games you want now then it definitely is a waste. For now, buy the games that are at the top of your "need to play" list, and once you finish those, buy the others. When the ps4 does come out, there will be huge price drops in all of those ps3 games you didn't buy yet.
My strategy is to buy most of the multiplayer online games I want now, so then when part of the playstation community moves over to the ps4, I still have all of the great single player experiences to enjoy. The only games I think you should buy now is the limited edition game trilogies (killzone, resistance, ezio, mass effect, etc.) since I don't think they will be made for much longer. But then again it's all up to your personal preference.
I hope this helped!