Maybe I'm a bit biased, having just bought one, but I'd choose the Sigma 30mm.
It doesn't look like the DA*200 would give you anything you couldn't achieve with your current setup, either from cropping the DA*50-130 or backing up with the DA*300. Perspective changes aren't as dramatic between telephotos either, so the DA*200 would primarily be providing an added layer of quality or convenience.
The Sigma, on the other hand, would give you shallower depth of field and more pleasing bokeh than what DA*16-50 can deliver. It seems the Sigma usually gets written off as a cheaper alternative for the FA31. However, while comparing images online, I ended up preferring the bokeh and contrast of the Sigma. Granted the FA31 obliterates the sigma once stopped down but, since a good zoom lens can rival a prime at smaller apertures, using a prime stopped down all the time seems almost a waste.
Having just returned home I haven't had the chance to play with the sigma yet, but here are two snapshots I took to test if the lens was OK. Both shots were wide open at f/1.4, processed with default settings in Silkypix.
Edit: I forgot to mention, if you do decide on the Sigma 30mm, 47st.Photo sells them on Ebay Buy it Now or Best Offer, and they will take an offer of 389.95.