I am not a PVD (or similar coatings) fan, but, with that strap, it does not look half bad.
Ending the work week wearing 1 of my Newmans (3rd from left)
The only genuine (Rolex) part is the movement. Everything else is clearly aftermarket. So either he's spinning the story about the 'very good rolex watch repair shop' or they are not very good.
Based on current values, the 16520 is likely going to be the better investment over time.
Generally, if a given model is collectible, older is better. In this case, the 16520 is also a bit less blingy, which, in today's market at least, also tips things in its favor.
In theory, the internal dimensions of DW 62xx Daytona cases for 7750s differ from those made for V72s (the external dimensions are the same), but the variations may be due more to the lack of QC & overall case-to-case variability than anything else. Either movement can be made to fit a given DW case with a bit of dremeling (which is often required anyway).
I believe it is just the 160x series of DJs, powered by 156x/157x movements, that have pie-pan dials. Earlier versions, powered by either 1036 or A.295/296 movements, & later versions, powered by 3035 movements, have flat dials.
Why replace the current crystal? There does not appear to be anything wrong with it & you open up the potential for problems by messing with it.
If it ain't broke..................
Nanuq is correct. Gen (ss) 1675s came fitted with a 24-530 crown & corresponding 24-5330 tube.
Whether these will fit a particular rep case, I cannot answer.