As of late I have been perusing photos of cocktail pinball machines, and I think I have come up with a fairly decent idea that will allow you to transform a beatup/halfway dead pinball machine into a nice playable game.
From what I have seen from my own pinball machines, flippers, pop bumpers and a few other assemlies are capable of operating fully independent of the actual pnball MPU. If you hold the game over relay open (or maybe it is closed), then they will work even if the machine has no boards in it at all.
So, lets say you pick up an absolutely trashed pinball machine that has board problems, and a garbage playfield, flaked up backglass, broken plastics, etc.
Are you with me so far? Good.
Now imagine a foosball table.
Remove all the little soccer guys from it.
Install the pinball transformer underneath the foosball playfield to power everything.
Install a set of flippers in front of each goal.
This alone will get you a decent little two player pinball pong.
Now, install the pop bumpers off the machine in some fun locations. Similarly install any slingshots or other mechanisms that are cpu independent (or that can be modified to be CPU independent) in more fun locations. Actually MOST pinball mechanisms can be modified to be CPU independent simply by rewiring them so that the leaf switch that normally tells the CPU to fire them, to simply close the connection to fire them without the CPU.
You can similarly install lots of lights (which can be always on, or can be blinked on or off when you hit targets or switches).
You MIGHT even be able to resuse some stuff like ramps.
Most pins should have enough stuff on them to make a fairly cool little two player game, which you could of course keep score on by using the old foosball scoring deally.
The only real issue would be laying out your stuff in such a manner that the ball won't get stuck on the flat playfield.