Hi Airconvent, thanks for the pics... hmm, probably if you have time (to trouble yourself again ;p) here is what I probably would do to compare both of these lens.
1. Take the same pic on 18mm at F3.5, and at F8 or F11, make sure same shutter speed/iso, crop 100% to pixel peep both photos at wide open and stop down. Crop at corners and centre of the pic.
2. Take the same pic on 55mm at F5.6, and at F8 or F11, make sure same shutter speed/iso, crop 100% to pixel peep both photos at wide open and stop down. Crop at corners and centre of the pic.
With this probably we can compare a bit on the sharpness and vigetting on the lens. Anyway the original kit is a pretty decent lens, I expect the new version to be better. Might need to test it on the K20D also to see how it resolve the details ;p