Depends on the wire-insulation class, I suppose... If you use class-A wire you'd be in trouble at 250 deg. F:

http://www.anotherpower.com/gallery/dinges/Leeson_5

I use class-H insulated wire but if one uses scrounged wire one can only guess at the temperature the insulation is rated for.

Using solvents to dissolve the glue wouldn't seem right to me either. How can you be sure the solvent doesn't damage the wire insulation ?

To the original poster:

If those were my coils I would cut my losses and wind new ones. Yes, copper is expensive. But you could at least sell the old coils for scrap value and recuperate some of the expenses. Reducing the number of the turns after they're bonded with glue (or even cast?) is an exercise in futility. (unless you used lousy glue to begin with).