Both the OPs and chickentenders images don't appear to be up to scratch....in the case of chickentenders image I can't find anything sharp anywhere in the frame, that's often motion blur...
In terms of cost...
compared with the Sigma 35 1.4, the 31 stacks up quite nicely, not as centre sharp better edge to edge sharpness, much lower CA which should lead to better microconstrast...
The Asunama is famous for it's "funky" bokeh, not usually a positive thing in a lens
Asanuma 28mm F2.8 - funky bokeh part II: Nikon SLR Lens Talk Forum: Digital Photography Review
The 31 on the other hand is famous for it's bokeh.
Neither or the images above approach what klaus at photo zone would call excellent... if that was truly the best I could do, I'd send it off to Pentax for calibration, possibly with the camera. But I have to also note, none of the images shown by the OP really show what the lens can do.
I don't know about where you live, but if I phone up the girl at Pentax today and send her the lens, in a week I'll have an estimate and in two weeks I'll have it back, checked out and cleaned, if nothing is wrong, for 25 bucks. My 21 only cost me $200 and it was dropped and needed new parts. Sometimes I think we should have a section here on what to do if your lens isn't performing up to spec... it's high end sensitive equipment, you just cannot buy it and forget it like it was a hammer. Getting the best use requires proper maintenance, but getting the best use also requires good technique. The big problem with evaluating pictures in a thread like this is it can be pretty hard to tell what's going on. What "should" be is irrelevant, if your gear isn't working up to scratch, get it serviced.
From my experience I know, my frustration level is not always a problem with faulty equipment... sometimes the problem is the little shortcuts I think I can get away with.