I have done a fair bit of work with my G1, while I have not done extensive comparisons w/ Kit lens versus my other ones, it goes something like this ..
The need for speed is not met by kit lens, nor in the 25mm length, in my price range, there is no M mount lens either, therefore, I use C mount lenses.
This is from a 25mm Wollensak 1.5
This is from a Kodak 25mm 1.4
There is no way the kit lens can do this.
In the 40mm range, I can afford the 40mm 1.4 CV, and it does a super job IMHO
This is no flash, hand held in a dark room. Again, no way that the kit lens can do this.
The 12mm/4.5 and the 25/4, and the 50mm Sumicron are not near as nice to me. and in fact, as soon as I get around to it, they will be on the for sale part of this site.
Much the same is true of the 12mm Cine lenses, they do have some cool looks, but they loose too much in the image circle. The C mount cheapos from surveillance cameras are very sharp, but have little character to me.
Hope this shows you some things you were looking for.
Dave