Don't forget that noise is a direct product of underexposure, and isn't necessarily inherit feature of higher ISO. You very well may know this already, just wanted to latch on to what you said and make sure you were going to get the result you want. Don't forget that going from 5.6 (at the 55mm length of your current lens) to 2.8 is the same two stops as 200 to 800, and ISO800 is extremely usable even on the K100, and much more so on the K20D and promised to be even better on the K-7, particularly with the improved shake reduction features to ensure proper exposure.
If your mind is made up, I won't further try and convince you, but the kit lens
already is a good quality general purpose lens, it's just not an mind-blowingly excellent one. Pentax doesn't really make any real low end lenses. The DA* lens are great lenses, that's true. Maybe I'm just not someone who succumbs easily to LBA, but my personal feeling is that lenses should only be bought to fill specific gaps for specific identified problems. On the other hand, there's something to be said for having at least one lens you just really love, and the DA* could be that. For me, it's my FA 35 f/2.0 and my SMC-M 50mm f/1.7.
*Edit* As a side note, I've been so satisfied with CameraLensRentals.com this week that I'm not sure I'll ever buy a top end lens again without
renting it first.