Using chance orbs to get specific uniques

The answer to is it worth it is sort of. In the long run you're probably better off saving up chances to buy said unique off of someone else, but the long run isn't long enough for a league usually, so chancing things is the way to go. Also I think it's fun.

The other side is maps that could go to unique maps, where you were just going to through and alch or trans on it anyway, so why not.

Yes, if you are SSF its extremely worthwhile, just decide what you are aiming for.
I started SSF'ing in Standard a month or two ago, got about 200ish hours in it. So far I've chanced a abyssus, lioneyes and bringer of rain with chance orbs going towards Onyx and Gold amulets as well. Sure they aint the chase T0 uniques like HH or Shavs. But in the SSF environment, in my opinion, its better to take the small - medium victories