You certainly should NOT buy a 1070 or 1080 graphics card RIGHT NOW.
The mining stuff went insane and currently (1-14-18) the price of a GTX 1070 that was $439 two weeks ago is $939. (Newegg)
FIVE HUNDRED DOLLAR PREMIUM to buy now.
The prices of 1060's aren't as bad, but walk away from high end graphics cards right now.
All we can do is hope that supply of the high end cards gets better, or that the graphics card manufacturers make mining specific cards that encourage miners to step away from gaming capable cards. Then the pricing will return to sane levels.
I'm waiting until late next year to buy. (subject to change if the mining market crashes and thousands of graphics cards get sold used on Ebay).