It really depends on what your goals are for the car.
There are a lot of drag subarus that are running unported heads and making monster power. See the problem with porting is that if you take too much material out you can easily crack a head.
I am currently porting my STI heads and took my old ones and cut them up into vertical slices. This way, you can see how far you can port safely without overdoing it.
If you decide to go with nice cams, a port n polish would be a nice but not necessary. If you are reving high, id port the hell out of em!