Tough deal. I've had two guitars that just don't/didn't agree with me - loved both and played the crap out of them, and both eventually led to [separate] injuries that had me not playing for about two years afterwards, each
Got rid of one (a PRS McCarty), but the other, an AVRI Tele, I still hold onto even though I don't play it - just sounds so good and looks so great that I can't let it go. Both were dream guitars for me...
Fortunately, I have other instruments that don't cause such issues. Sucks, but some things just aren't meant to be.
Still, one reason I keep the Tele is that it has a bolt-on neck and so I could get a new, flatter radiused neck for it (which would solve the particular problem I have with that one). I still plan to do it, but haven't gotten around to tackling that particular project yet.
Similarly, if you reaaally dig that Mustang, you
could make it work. Have someone strip the finish and cut/sand down the dimensions to match the Bronco, then have it re-surf greened. Or, get a new body custom made for it to the Bronco's specs, and have the guy put your Mustang's guts in the new body, too. Or put the Mustang neck on a Bronco body and have someone route the body and carry over the electronics for you. Etc.
When it comes down to it, Fenders are an aggregation of removable parts, and so you could accordingly keep the parts you like and replace the parts you don't like with other parts that suit you better (or even custom-made parts that suit you perfectly).
Or, like I did with my McCarty, you could move on despite digging it so much.
Tough choices, but at least you already have some instruments you know you can play.
Good luck!