Discoloration, scratches and tiny holes
call a glazer.
Sounds like your tub is degrading fast, I agree replace it. You can also go to an architectural recycler and find a used cast iron tub or steel one.
Fiberglass is a hard one to repair. Keep in mind that a lot of automobiles have fiberglass bumpers or fenders. Try an automotive polishing compound. Talk to the manager at Autozone or automotive supply near you. You'll want something you can use to buff out the scratches and leave polished looking. If you do this, take care in stepping in the tub at first so you don't slip. Use a rubber mat at first for a while.