Keep it for a long time. Reasons to keep it:
A) you will eventually crash that stick, and you'll need something to fly while you re-build it
B) you may have a friend who wants to learn and you can teach him/her on it
C) trainers are always fun to go back to
D) some days you might feel lazy and just want to put around the sky
E) you might want some experience making mods and building--start with your trainer. for example, make it a bolt on wing, or add flaps, or add dual aileron servos, or just stuff like that. Easy way to get into mods and learn more about planes.
I'm sure the list can be added to.
I kept mine until I had over 7 or 8 planes in the hanger. now my stick is my "putter arounder." Then, and only then, I donated it to the club.