The WRX runs with 440cc injectors, and I don't think it needs any attention anytime soon. They are good for up to 300hp before they need to be pampered.
I changed my tires to Michellin Pilots. They cost a whole lot more but they grip very nicely. I took the car up to Tahoe this weekend and I was very impressed with the grip in snow and ice. The RE92's are junk.
If you want more power fast, get a boost controller, preferably an electronic one like Apex-i or Blitz. Run a modest 16 psi, and that will keep the turbo happy if you use good engine oil and avoid long WOT.
The Cobbs system is a good upgrade, but it is more complicated and I would stay away from it until the warranty expires. Exhaust and up pipes are both very effective, and the mid-range response is tremendous.
I am not a track person so I find no need to lower and beef the suspension. The chasis is stiff enough as is and I like the way the car behaves the way it is.