I would think a spectator would get more out of it then a player. How many of you look at the screen a lot while playing? I've found myself glancing at the display more lately than before but it is still very quick glances. Most of the time I'm glued to the playfield to hit the ball and keep up with what ramp shot, target, etc. I need to try to hit next.
The screens on the Williams 2000 machines (Star Wars and Revenge from Mars) get seen a lot because they are integral to the game and reflected so they appear on the playfield. I really don't see screens in the back box doing much from a player's perspective.
At least for a traditional type pinball machine; personally, I would be interested in a Williams 2000 type setup but not an LCD in a backbox. For a video pinball machine, such as a Visual Pinball or Future Pinball setup, I can see an LCD in the backbox to emulate / display various things.