Plex or glass will reflect light. My cab, with plex, is in the kitchen and if I have the ceiling light on it causes enough reflection to be annoying. But I have noticed the same thing when playing machines in the arcades. Cab placement is the key.
I too have a Nintendo Vs, but a cocktail version. They used plex, then glass and yes its very dark and the screen reflects overhead lights badly.
As far as tempered vs regular glass, the man I bought my cab from has been in the business for decades and uses plain 1/4" thick glass, no injury incidents yet.
So for a household with unruly kids or idiot adults I suppose tempered glass would have to be the way to go.
Since I can't afford to "get a new piece" of plex @ $20 a pop whenever it gets scratched, I choose to work a little smarter than before and cover the plex with some glass.
Its held up for over 20 years in the Nintendo Vs, seems like a good idea to me!
Anyway, just my experience, hope it helps. ARCADIAC!