If you want to trade your car in for a car that would be better for track use, than you should trade it in for an Evo9, not an STI.
The '09 trannies aren't as fragile as they were in the past. Some of the internals have been shot-peened to make them stronger.
You shouldn't be so worried though- Your car is brand new, you have a warranty.
Worst case scenario- You bust your tranny and your warranty is voided due to abuse. That's when you decide to rebuild it with better parts, or swap to an STI trans. Either way, you still save money.
You will always take a hard hit trading in a new car. New for used / New for New...doesn't matter. You will lose money.