It would absolutely be worth it. AMD has come a long way, and driver problems and such are no more of a problem for AMD cards than Nvidia. As you said, your last experience with AMD was many years ago--it's not many years ago any longer. It's now. You should switch to the 6450 if only for the fact that the hardware is newer, cooler, and runs more efficiently. The gaming performance won't be super spectacular, but it certainly won't be a step down from what you have now.