That's a very nice version of the shuttle!  I really like your weathering.  Its not over the top but just enough.  And on the subject of the MPC shuttle kit; I've built it and its a train wreck!  Its gigantic for one thing, which may be good except that the size (length of the wings) and the age and thinness of the plastic make it a warped nightmare.  I'm looking into the newer smaller kit to super detail and paint it.  Hope it turns out as good as yours!