Without pics, I can't tell if it's worth it. As long as the car never crashed, you can't go wrong with Roush mustangs.
With that budget, if you want to go with mustangs, there will be multi choise.

1st, if you like a fast car on the straght line, find a GT500;
2nd, if you like a mustang can handle corners, go with a Roush Stage 3;
3rd, if you want to project a mustang and have fun with it, either a regular GT or the V6 will be good..

 

Yupp, I agree, great motor, decent interior, average looks at best..They should have never named it the GTO...I love the GTO's from the sixty's, but this is not even remotely close to their style..

 

a wide range, depends on your taste.
impo, 15-20k makes fot a nice 05-09 mustang gt, i preferred the convertible, others don't.
for 30k i would go for a 05 or later c6 vette.