When I had my turbo Eclipse, I kept just about everything I changed with aftermarkets parts, and glad I did. When the car was totalled in an accident, the body shop allowed me to put the car back to stk (as much as I could). I was able to sell the aftermarket parts the summed up to about $2000. If I wouldn't have kept those stk parts, I would've lost that money.

My Z may be getting purchased back by Nissan (long story) and if it does, the Injen exhaust is coming off and the stk going back on.

I would keep the stk parts.