Hard to say if it's worth it. Right now the return on investment is quite long, which is only really going to be changed by a sharp increase in the value of a coin. You must then ask yourself: would it have been more worth it to just invest the same money in the coin in the first place?
I'd advise against 7970s if you do decide to mine, however. 7950s offer much better hash rates for the cost/power draw.