So assume you have a couple of lenses you like, and some you don't. An easy assumption since nearly every camera user will invent reasons to rework the kit, sometimes on a mere whim or rumor! In any case, how does one go about rearranging the kit, and find true imaging happiness?
I have a few great primes in the DA21 and DA70 Limiteds plus a nice Sigma 105mm macro. I can stick a prime in between the Limiteds (35 or 40mm?), or choose the new 20-40mm Limited zoom and release the DA21 back into the wild. Another option is a 17-50mm f/2.8, which would go nicely with the 70 and 105. I could also abandon Pentax and pick a Sigma or Tamron 28-70 or 28-75 zoom at f/2.8, which could send the DA70 packing¹.
I really dislike Pentax' forcing a lens change around 50mm (16-45, 16-50, 18-55 + 50-135, 50-200, 55-300 etc.)² as I find the 50mm zone worth moving past in one direction or another. This suggests that I'm a good candidate for their upcoming DA 17-85mm± offering, which should appear in 2014. In the meantime a DA35/2.4 would fill my gap with the least expense - assuming a DA40xs does not magically appear.
A few shots with the DA50-200 have shown how the primes obliterate this compact lens - but what after that will I be willing to carry? Actually the Sigma 100-300 can cover that ground for a while despite its relatively slow f/4.5-6.7 aperture, though the HD 55-300WR would be a good option too. I owned and liked the Sigma 50-150, and the DA* 50-135 does drop into my price range at times. This is less of a priority so I can punt on telephoto decisions for now - but I'd think a weather-resistant 17-85 + 100-300mm would make a simple and impressive pair most days!
P.S. The magic worked: I found a used DA40XS for less than the price of a used DA35/2.4! I did not expect that, but I'll cheerfully take it. Most reviews say this is an optical clone of the Limited lens without quick shift, but some like it a lot less. When the time comes it can be sold with my K-01 and bring it back to its original complete and bizarre nature. :^)
¹ I do have a Quantaray 28-90 with 1:2 macro, but it's f/5.6 at the long end, and it flares some when the light is wrong.
² the DA 17-70 bridges that gap, but with no WR I'll wait and manage with primes.