I am very sure I am just an amateur.For me, the biggest limiting factor is that I'm afraid to take pictures of people, like maybe those 'ah peks' sitting around and doing nothing, wait I take picture of them they kick up a fuss. Hmmm, are you sure you are an amateur? Doesn't seem like it. Agree, 50mm 1.4 is too tight, and was considering the Sigma 30 1.4 until you mentioned the QC problems. Ah well, primes can wait, no $$$ now....
Btw, saw your post in BNS advertising your 70-200, you decided on selling it? Wonderful lens if you ask me, you have already made up your mind on selling it?

If you are worried about the QC of Sigma, you can spend a little more to buy a unit with local warranty. The front/back focusing problem can be fixed by bringing the lens and your camera body to Sigma Service Center for calibration. If I am not mistaken, a local set is entitled to two free calibrations during the 3-year warranty period. Subsequent or out-of-warranty calibrations cost about $120 each.
You should also keep in mind that reviewers use specialized tools under strictly-controlled conditions to determine the optical qualities of the lens. Depending on how you use the lens, certain qualities may matter much more than others in real-life usage. If you usually shoot a lens wide open to isolate the subject against a blurred background, would you even notice the soft image corners which are out-of-focus in the first place?