Have we reached the point with pinball where "barn find" games are the holy grails? The value of the game should be in how it looks and how it plays. If it is restored or original, if it looks and plays like crap it is not going to be worth as much. If the original boards have been repaired so many times that they are more bus wire than pcb is it still better than a good quality new replacement? If the playfield has been correctly restored and cleared, is it less valuable than letting the original be played to the wood?
People need to figure out if they are in this for the games or the collectible value. We are in a price bubble due to the resurgence of interest in pinball.
If you are in it for the love of the machines and playing pinball, restore it to the level you are comfortable with and so that it plays the way you want it to without worrying about the value when you go to sell it. Your investment is for your personal enjoyment.
If you are in this as an investment, good luck with that. Buy them now and do not take them out of their packages. Hope that in a few years they are worth more than beanie babies.