Opinions always differ but for me once you get past 71-72 I don't have much interest in Gibson before the 80's again. Like any guitar, if it speaks to you, your hand loves the neck, it sounds great, only you can ascertain it's worth. I know there's some gems from the 70's but I find them to be anomalies rather than common. But I've played a few 60's SG's where I thought who would want this...and it's a few thousand!? No era is a guarantee of awesome or suckage. See if you can get it cheaper and you can always get it re-finished.
If you just stumbled upon it maybe wait to see if a black one from the same era shows up down the road. There's a lot to be said for that you got to play it in your hands though vs finding a black one that you get online without playing it...
sucks doesn't it..