I welcome repros in all cases. Sometime repros are functionally better.
Playfields - I've bought around a dozen playfields from CPR or IPB over the years, and they breathe life into games with tired and worn playfields. I don't believe in overlays - they are rubbish. The only issue I have with reproduction playfields on SS games is that the clearcoat is WAAAAY too glossy. Beats worn to wood playfields anyday.
Backglasses / Translites - The screenprinted Backglass from CPR are simply stunning. Again, great for missing or damaged glass. Translites are are different story as there is no quality control and some look like they are printed on an crappy inkjet !
Plastics - Always needed. I cannot get enough of them !'
For someone like me, I deliberately target projects that "I know" are having parts reproduced. Fathom, KISS (2), EBD, Medusa, Paragon, Eight Ball, Flight 2000, Flash Gordon - just to name a few. All need "something" replaced. The aim will be to own the best possible example of each game. This is not possible without repros.
I welcome them, as long as they have quality control - which typically means that a few collectors have checked and tested the item being reproduced.
Other cosmetic parts such as drop target and bumper caps are absolutely necessary.
I've seen NOS playfields and like anything made of wood and stored for 30 - 40 years will show its age.