I think it might work, and could be a profitable thing since it would require regular updates and new editions. I'm thinking primarily of something like the ones I used to get for comic books. I guess if we didn't want to put the time in to do a comprehensive book, we could just focus on the most valuable or rarest items. Maybe it could be based around platforms, so you'd get info on how and what to collect for the Apple II vs. IBM PC, etc. The hard part for me would be tracking all the various ebay auctions to get a fair sense of what something is worth. You'd have to by necessity track many, many auctions over an extended period of time to arrive at that. I'm assuming there is probably already tracking software of some sort out there for that purpose, so it might not actually be difficult.