True. The few auctions I've been to were flooded with multi-cades, generally homemade, and priced well above dedicated original cabs. There are plenty of half-assed home projects with what looks like ink-jet printouts stuck on as side artwork with requests of $1000+ in classified ads. I don't know what some of them pull in, but it's enough to where these things still show up and are clearly different machines.
The cocktail I have was a Williams converted to Techmo with Rygar inside. I'd like to convert back to a Williams with a cocktail multi-board to avoid PCB swapping. The alternative is to custom build a few PCB slots inside the machine and fill them, moving the harness around as needed. It's very limited but keeps original hardware. I have no plans on simply flipping the arcade on Craigslist once I'm done as many others do.