I installed my STi RA springs a couple of days ago along with Koni strut inserts. This is a bargain-basement setup - I only spent $720 plus shipping. My other mods are the Whiteline ALK and Rear Swaybar.
Handling is still a question mark as I still have my snow tires on the car. That being said, pitch and roll is dramatically reduced and the front end feels very planted with a dead-neutral balance with struts at 50% adjustment. I'll let you know more about handling when my Yokohamas arrive.
Install was straight-forward but time consuming. For me (I'm slow) the hacking and drilling required to fit the new dampers to the OE strut housings probably added close to 2 hours to the job. The cool thing about the Koni design is that it leaves a great deal of room for error in the install.
The ride quality is absolutely spectacular. I'd rate it MUCH better than stock. My wife absolutely loves it. While people who like to be isolated from the road completely might not like it, it is incredibly smooth. You feel all the little bumps, cracks, undulations, etc but the struts just soak them up really smoothly. I was fully prepared to trade ride quality for handling but this has not happened. Every other car I've done this sort of upgrade to suffered in the ride department. I think I have the Imprezas stiff chassis to thank for this. I'm glad I didn't opt for softer springs (e.g. STi Lowering, Eibach or Prodrive).
I'm now convinced that Subaru got the valving wrong on the stock struts. I'd get jarred by pavement seams and cracks, but it would wallow around in the corners. Koni got it right. I feel cracks and seams (wouldn't want it any other way) but it rides really smooth over them while staying rock-steady in the corners.
If anything, the improved ride reminds me of an Burly old V8 CJ-5 I had once, nicknamed "The Blue Meanie" by the previous owner. A CJ-5?!?! Well obviously that CJ was never going to handle or ride well on the pavement, but that's not why I bought it - it was a 'wheelin' beast! I put a set of heavy-duty leaf springs on it with adjustable Rancho RS9000 shocks. When going off road you could crank the RS9000s all the way to full stiff and the ride would become incredibly smooth. It would ride like a Cadillac while haullin' ass down rocky rutted out trails and catch good air over yumps and charge confidently through deep rocky water crossings. I ain't talkin' about the smooth dirt ROADS that people on ClubWRX call "off-road" - I'm talking about serious world-class jeep-trails. The kind that break those wimpy SUVs in less than a mile!
The Subaru now reminds me of that. Very little pitch and roll and incredible confidence. I live in a subdivision built on the side of a mountain and we have these deep drainage troughs crossing every intersection. I used to crawl through them but now I can charge through them confident that the nose won't dip way down and crash into the other side of the trough. Same for speed bumps. I can see why Rallispec rates the full STi RA setup as a great rally-cross setup.
There is no noise, vibration, or harshness. No reason at all for a passenger to think it runs anything other than stock suspension.
This combo on my Wagon lowered me more than most people report with the full STi setup. A little more than 1/2 inch front and rear.
More to come when I get real rubber on the car.