Using your numbers with whattomine I get the following:
1x rx580 8gb daily return mining Ethash @ 130 watts:
$0.46 revenue
$0.14 profit
1x 1660 or 1660ti or 1070 or P106-100 daily return mining RVN @ 106 watts:
$0.64 revenue
$0.38 profit
Used P106-100 are the same price as used Rx580 8gb; its a no brainer: over 2x profit and way more mineable algos.
New rx580 8gb are $180 lowest I can find. The second you buy this, its resale value is $100.
New 1660s are $220 and its resale value is $200 at worst; its a no brainer.That's the big issue (bolded), rx cards are so flooded on the second hand market, I could hardly even sell a like new rx470, they're not even worth $100 these days lol -- and this point is profits aside