Better just replace your existing head gaskets unless you're thinking of getting more power out of it. That's what I would do if I were you, at the very least, it'll be good for another 170 - 180 K, which will be the life of the car.

Now, if you plan on keeping the car, and wanting a bit more performance, then I'd go with the complete swap route using a USDM WRX engine mated to your drivetrain.