To me, the value of a 980 is 90% of whatever a 480 is going for and no higher.
If someone had a 980 and wanted to sell it to buy a 1080 I'd be tempted to offer $200-220.
Higher performance reference version, better efficiency, much larger overclocking potential (i.e., it beats/rivals an OC'ed Fury), better memory compression tech and still less DX11 overhead. Not to mention better idle and blu-ray power consumption. Why is it worth less than a 480? Please don't say anything about performance a two years from now.
The only real advantage the 480 has is DP 1.4 and who knows when that's going to be important.