I've got two rigs of 570's that I have basically dismantled. Whilst I could run them for the sake of it, at 16ct/kwh it's a zero-sum game. If someone rocked up giving me £50 for each 570 I'd give them the whole batch (14 of'em).
For what? Rigs taking up too much space?
Every time the price of the coin there are similar threads/questions. If the graphics card has already paid for itself it is not necessary to touch them, let them be "for the future".
470/480-570/580 is not so outdated to be in a hurry to change them. There are people who still use 7950/70.
There will be another increase in the cost of ETH (or any other coin that is profitable to produce) and the graphics card will again rise in price.