I agree that the Nexstar covering isn't the best. It's a trainer though so the life expentancy isn't the same as somebodys 3'rd or 4th plane. Still, it would be kind of cool to recover one to set it apart from the others. I personally see two problems with doing it. First, removing the old covering could pull up some balsa here and there and/or leave adhesive residue behind. It could be a lot of work to remove and get the plane nice, clean and smooth. Second, the control surfaces come pre-hinged if I rememeber correctly. This means that is won't be easy to cover the LE of each surface or the TE of the wing, stab, etc. I'm not syaing it can't be done though. Monokote is good but uou may also want to look at Hangar-9 Ultracoat. It is good stuff and easy to work with.

Whatever you do, don't try to totally recover the plane over the top of the existing covering. Your wrinkles and stuff will still be underneath. The two coverings may stick and shrink at different temperatures, causing huge problems. You'll just add unnecessary weight.

Personally, I'd just run a sealing iron over the whole thing (be careful around the decals) and add a little CA or clear nail polish to areas you think might lift up.