Hi PinballFever.
It sounds like you have a realistic and good attitude about the repair and sales options. I find that resale value varies by a very wide margin from region to region. Best to look at the current offerings at your local Craigs List (And how long they've been listed) for possible ball park figures.

A 4 player game is not any more difficult to troubleshoot than a 1 or 2 player game IMHO. It is basically the same circuits as a 1 player game except routed through a player-up switch (Player Unit). It can appear intimidating but once you have a good grasp of a 1 player sequence of operation then you should be able to transverse over to a 2 or 4 player game without too much trouble.
With few exceptions, a person can do a real good job repairing a 4 player game and enjoy trouble-free service between every maintenance cycle. On the other hand, the same person can do a hurried up crappy job on a 1 player game and have constant trouble. Yes, a 4 player game can appear intimidating for all the extra reels and the player unit but if you can separate it into its individual player (1-4) circuits then it can make more sense.

Here's my attempt to simplify the complicated reset sequence of your game:

I'm not any great artist (you saw my BG repair) yet I found the airbrush very easy to use, especially with acrylic paints (Water based). I generally use 20-40PSI in my cheap Badger 350 single action airbrush. You don't need a fancy compressor but you will need one either designed for airbrushes or one with a reservoir tank.

On a PF, I think acrylics are good for filling in minor planking, then followed when thoroughly dry with waxing. However if you need to airbrush... which would cover a large surface then I wouldn't expect the acrylic paint to withstand the steel ball, so that's when I clear coat.