Should I polish my pre-moon speedmaster and replace the bracelet?

Polish it if you want.

I personally wouldn’t choose to polish it for many of the reasons shared by others.

You would be better off selling the watch and buying a brand new Speedmaster with the proceeds to make your own memories with if you want an unblemished watch.

That said, if you DO choose to polish it, I would only allow someone like LA Watchwerks to do it, as they are extremely familiar with working on vintage watches and are a very reputable shop. If you take it to a random watchmaker, it will almost definitely be a disaster. taking it somewhere like LA WW will be expensive and frankly the idea of trying to make an old watch look new largely defeats the purpose.

I'm with everyone else. If it was my grandfather's watch, I'd never polish it. Keep it as a memento to your grandfather, and keep it as original as possible.