I have the L versio but I can't compare it with the non-L version.
As many stated before me, the L is a very good lens, that I use very often as standard lens, since I like go around catching details of the world around me (a beautiful dish or drink, a flower, the texture of a stone wall etc.), obviously without a tripod.
By the way, prices never follow the same curve of performances, in photography as in every technology. To get ten percent more power in a car you will spend well more then ten percent...