I've got the 50mm F1.7 and the Sigma 30mm F1.4. I agree that the Sigma 30 is more what the Minolta 50mm was originally designed to be as a prime lens - that 50mm focal length without a crop factor is fairly good for overall walkaround photography, but at 75mm it does become more of a specialized lens for portrait, closeup, or low light work. The Sigma 30mm I can use more as a walkaround lens.
However, for the money I'd definitely recommend picking up the 50mm F1.7. It is quite sharp and usable wide open, which really for me speaks to its primary use - for low light/high ISO shooting. And stopped down, it is razor sharp. It focuses fast, isn't really prone to any CA, and is a pretty decent portrait lens with nice bokeh. At $60-100, it's an easy purchase to justify, even if eventually you end up picking up the Sigma 30mm or something similar.
I have to agree. For the money it's very hard to go wrong. Not sure I'm willing to spend over $400 for the Sigma just yet, but it sounds like with the Minolta, you can't really go wrong. Worst case scenario - you don't use it and you sell it for what you paid for it.