A reputable and frequent eBay seller of Apple hardware recently auctioned five stock 2012 quad core i7 mac minis. This model is the gold standard configuration. Low price was $535, high price $580, average price $559. The valuation is a huge a drop from about $680 early in 2016 and $730 in 2015. The drop suggests to me buyers anticipate new models soon, which makes them unwilling to pay premium prices for the 2012 models at least until they know the specs on the 2016 models.