Oi! I hope my suggestion wasn't considered a bodge job!
Plenty of manufacturers use plastic inserts (some threaded, and some plain) and not just on motor vehicles. Under wing inserts, landing panel fixings, and numerous box section applications, where ever it's a blind hole relatively light fix, location?
The plastic plugs I have used time after time, where I was unable to access the reverse side of the fixing. A common fault with captive nuts,(light loaded) in box sections, where the spring steel cage that retains the nut itself just tears up, when the threaded bolt/screw and nut rust together. Normally set in a square hole?
If access is available to the nut retaining side, then bronze welding, or a bead or two of mig, on the nut faces, effects a permanent professional fix. The problem with all compressed (mushroomed) threaded inserts is again one of corrosion,( needs copper grease applied first to the screw/bolt thread,) which if allowed to badly corrode, seize, will present problems again if allowed to rust with exposure to salt and moisture. I'll lookout the plugs I have used to great effect, when I dare venture into that cold old workshop again, and check the type.