My thoughts on clear coating playfields  - I'm not a huge proponent, which I know is an unpopular stance.
Hear me out, though: ball travel is all important in any flipper game.  Knowing how the ball will react is also critical.  When the game is being played with a clear coated playfield, the ball reacts as if it is skating on a layer of ice above the wood.  Spin and travel are not as they normally would be for that title.  Ball travel is also critical for the bingo: one of your measures of control is knowing how the ball will react when striking a post or spring. 
There are exceptions to my thought - if you do playfield touch-ups, you will want to clear coat over top of the touch-ups to help preserve the new artwork.  The original artwork has a shellac or other lacquer finish that has preserved the artwork for 50-60 even 70 years - why mess with success?
 
I ensure that my games are waxed regularly, and this preserves their paint.