The four digit Contenders are somewhat collectable, especially the very early ones or those in outstanding condition. Original flat side frames (no etching) or those with eagle pattern etching are especially collectable. If I understand your description of your frame, its condition is such that, unless it's a flat side or eagle, its collector value would be negligible, but that's just MHO. Also, you need to understand that barrel interchangability on the early frames is a sometimes thing. I have a few four digit frames, and most of them will not accept stepped bottom barrels. They work fine with flat bottom barrels. Sometimes you can change out the trigger guard with a somewhat newer frame and they will accept stepped bottom barrels. Of course, they can be modified to the easy open feature, in which case they accept just about any barrel, but this destroys collectability. It sounds to me like you have a shooter anyway, so if it were mine I would do to it what ever I wanted to in terms of refinishing or reworking. On the other hand, someone on this board may decide to offer you a premium for the four digit frame; if so, I'd take it and get me a new G2. As I said, all this is just my opinion - others may differ.
RonF