having an i5 7600k + rx 480 8gb (single)
planning to upgrade to 2 rx 480 within the next 6 months.
worth it ?
Maybe. Some games benefit from crossfired 480s and others won't. Scaling obviously won't be 100%. Power consumption will be doubled. If I were in your position I would sell my 480 and invest in a 1070. One card, all games, less power consumption.
Sell the RX 480 and buy a single gtx 1080. If you crossfire the RX 480 consider also that you may need a new psu as well. The power draw will be quite higher, over 300 watts, without overclock. GTX 1080 beats the RX 480 in crossfire for most of the gaming titles.