Find a tuner who has a track record with auto's. Matt from Kido-Racing (in the commercial section of the For Sale thread) is doing my ECU DBW tuning and it is improving with each ROM image. Hard tuning the TCU and Valve body did not work. There are too many parameters of the ECU that have direct impact on the transmission performance.
Without doubt, before any mods to the tranny, go with a tuner like Matt who knows the intricate dependencies between ECU and transmission like no other tuner I have engaged with.
After my experience with Valve Body mods, I would say don't waste your time. Save the money (about $1400) and put it toward other mods or maintenance (could also be applied to wife, girlfriend or significant other).
Alternatively, use it to buy a notebook computer and a Tactrix Cable to connect to your OBDII port which then facilitates the whole ownership/tuning experience if you want to go that route with an experienced and knowledgeable tuner. Learn how to read and write to your ECU (at your risk of course) through the RomRaider and Open ECU forums.
If and when your tranny does need to have an overhaul, then I would consider the upgraded friction plates and additional ones in each clutch pack. But only if you are chasing high torque and power numbers. Stock will not need it. Costs for me were around $3800 for the transmission and centre diff to have all clutch packs upgraded while also applying a standard Subaru overhaul kit. Car was off the road for 5 weeks (ouch)!
