Also, it is difficult to properly liquidate a unique collection like that. A live auction wouldn't bring a fraction of the true value (simply not enough truly interested people would be able to attend). Ebay wouldn't cut it, unless they took years to do it (list 200 Atari prototype/alternate/NOS games at once, and watch as they sell dirt cheap because they are competing with each other).
But it is cool to have a unique piece or two. My Victory pin is a prototype/VERY EARLY production model that has the playfield graphics in a totally different style than every other Victory I have ever seen. Meanwhile my buddy Dave's Doctor Who pin is one of the prototypes with the factory moving Dalek head.
But, (except for pins) prototypes are really mostly just conversation pieces more than anything else. Games that were never released were usually not released for a reason, and games that WERE released usually have protos that look like a poor conversion from whatever the game company was shipping at that time.