Interesting question but one for which there may be a partial answer: The Quad 405 was produced in relatively large numbers and still appears to be in demand, to the extent that clone circuit boards are readily available. A search of eBay reveals a number of small businesses offering amplifiers using these boards in a variety of different cases. One example, offered as “used”, was clearly a poor attempt at looking original but two others had taken a different approach. Of these one was a simple box, minimalist in the extreme and the second was a two box design with the PSU separate from the amplifier. What we have is essentially the same amplifier in four different cases, on the day I looked, so one might conclude some buyers don’t particularly like the original case and prefer to buy a “pretty” case.
Unfortunately the disparity in production numbers means there isn’t a definitive answer to your question but it would appear that some people will pay more for the pretty case. Of course they might be paying more for a new amplifier rather than risk buying a used one.
