Quoted from Monk:For what it's worth, I can see the wood grain on my TSPP playfield. I don't think it gets worse or effects the game at all. It is a bit of a bummer though.
My WOZ had the same thing, and it was never an issue there either. And it's less noticeable when I shut the work lights off (I have lights right over the games that I usually only have on when I'm working on them).
As long as the playfield doesn't start ghosting or chipping it will be fine.