I'm running OEM STi springs with gutted WRX struts and Koni inserts. The ride quality is very nice, same if not better than that of a stock STi. There is plenty of suspension travel for less-than-ideal roads we have here. I am able to adjust rebound, but compression is static. I am not using camber plates. For a daily driven street car that will see some track, I think this setup is very nice. Handling is very nice for it being a Forester, STis will always have an advantage due to better drivetrain (torsen diffs, DCCD). In capable hands (not mine), I believe my car can do pretty well on the track. If you were to buy the inserts new and springs/donor struts used, you could have a similar setup for under $800 -- $600 for Konis from tirerack, $100 for donor struts (I got a set for $50) and $100 for STi springs (I got a set for $60 or so). Ride height will not be adjustable, but you can raise it a bit using tophat spacers.
You can probably get a set of '04 STi struts with OEM springs for $200-$300. It should be very similar to my setup, and IMO for the money is very hard to beat.
Good coilovers will give you more adjustability. They will be in the $2,000 range. Out of the box, the springs they will come with will probably be much stiffer, depending on the valving this may mean a harsher ride on bumpy roads. I would love to try a nice set of coilovers on my car, but have not had a chance to do that yet due to cost.
Stan