Eh, I've got my 1070 mining some altcoin right now. Might as well make some extra cash on it, my electricity is cheap, and we need heating anyway lol.
Though I didn't buy my 1070 for that purpose, which is the difference.
The thing is though... when you can make 500$ a year with a GTX 1070 from basically doing nothing, ofcourse people will be willing to pay more than MSRP for it. It won't change unless cryptos die, all algorithms are asic'd, or Nvidia and AMD all of a sudden were to flood the market with GPUs (against their interest, they make money of this lol).