Rumor is that the entry price for the 570/580 rebrand will be slightly lower than the 470/480 was but its unknown for sure and we won't know for at least another month right now.
I just jumped on a deal yesterday for some sapphire 480s with the 7000mhz memory for a new rig I'm building because the price was right.
Right now with the current price increases that are occuring on ETH, waiting a month is highly questionable whether or not that would be the better play.
My bet is, if you can get your GPU's at the right price, the increased return you'll get between now and next 30 days will outweigh any potential cost savings there may be by waiting a month to buy a RX4xx at a cheaper price or purchase an RX5xx that performs slightly better.
I was thinking the same thing. I'm pulling in around $2 a card a day. So 30 days is $60 a card. I don't think the resale value of the rx470's will drop that much once the RX5xx's come out. I think I'm just going to order a couple cards and mine away while the sun is shining. Thanks guys for the input.