I sympathise with you on your 16-50 plight. I only tried 2 copies before I gave up and swapped for a 12-24, but 4 copies ...
.
The glass half empty view is that it is ridiculous that Pentax can't produce a decent wide-normal quality zoom, what is possibly the most useful/needed lens in any manufacturers lineup. The glass half-full view is that the primes in this range are superb and the choices are numerious.
If it's wide you want then I think the DA15 is a great fit if you take mainly landscapes. It's a joy to use and produces terrific images. I like my DA21 too, it's actually a more versatile focal length than the 15 if it's mainly shots of people that you want to take.
Of course the DA12-24 is an option too. I've just returned from a trip having taken over 4,000 photos with that lens in just a few weeks. The experience confirmed again that while the lens has fantastic image quality and a great travel lens, I couldn't wait to get it off my camera when I got home and I doubt I'll be touching it again for some time. It's just not an enjoyable lens to use compared to the DA15 & DA21, it's too big and the hood is a royal PITA.
My tip on the most under rated limited lens though is the DA70, not that it has a bad reputation by any means, but I just can't say enough good things about it. The IQ is just stunning as is the handling. I think I prefer it to my FA77 which cost me a whole lot more.
Good luck with your choice....