18-55 is not wide compared with the other lenses you mentioned there. So, I can't see this being the answer, unless you don't really want an ultra wide.
So you need to decide what angle of view you need first: 10mm is a vastly wide lens - you can stand on the footpath in front of skyscrapers and fit the whole thing in.
There is not much in the way of weather resistant lenses that are also wide. Only the DA* 16-50, but again, not an 'ultra wide', just 'wide' and not cheap either.
I have the 18-55wr and it's OK outdoors in daylight, but when using the flash I really miss having a bit more aperture, as it's often too slow for decent flash photography. It's definitely too slow when teamed with the K7 for high iso shooting. I mainly use it if it's raining or if I just want to pack a small kit. The quick shift focus is a nice feature, though.
I did a few calculations to help with field of view:
28mm = 54.5 degrees (diagonal)
24 = 62
18 = 77
17 = 80.6
16 = 84
15 = 87.7
14 = 91.7
12 = 100.4
10 = 110.5
8 = 122
Hope this helps choosing.