TL;DR - Hash/Watt is a necessary consideration for everyone
I am in the process of replacing power guzzling cards like 560Ti 448 core edition, 660Ti with the new Maxwell GTX
750Ti line of cards.
I won't be replacing the expensive beasts like GTX 780Ti, GTX 780, Asus MARS anytime soon because they haven't
really done enough work yet, so throwing them out at this point is not justified

Christian