Like so many, when I bought my K-7 with this kit lens, I had no idea why this lens was, well to put it plainly, pretty craptacular.
If you go read the review at photozone, the results at "wide open" are fairly abysimal:
photozone test report
I of course didn't know that at 5.6 on the "long end" this lens was really only useful for outdoor photography in broad daylight. Fortunately due to the $100 rebate Pentax was running at the time it was practically free.
This lens was quickly replaced by the DA* 16-50mm.
However I've discovered a nifty feature of this lens that keeps it in my (secondary) bag. At 55mm this lens can stop down to a whopping F40.
I've got no other lenses in my bag of tricks that I can stop down to this pinhole of light, and so it makes this lens an interesting option for shooting water with associated scenery and nighttime light motion. As pointed out in the photozone.de article, it's resolution is decent and the other problems tend to go away once stopped down.
Of course, you'll need a tripod for that 15" water exposure at F40.
Conclusion: before you go selling that kit lens for $40, consider that it might be able to do something no other lens in your collection can do.