Well Paducah Kentucky is pretty much considered a quilters "Mecca" with it being the headquarters for American Quilters Society the Quilt museum, the annual show and of course Hancocks of Paducah and EB Quilt in a Day shop. Utah seems to have an abundance of super talented quilters. Must be something in the air.
Then there are all the Amish and Mennonite communities for having great quilt shops at reasonable prices for fabric. I think loads of different areas have different offerings and there are always big national shows in regional areas of the US that are within a days travel for many US quilters.
But if I had the means to live comfortably anywhere I wanted, I don't think I would center my choices on quilting. I can always travel to a workshop for a well known instructor and I order fabric on line most of the time anyways. I would love to live somewhere where I had drop dead gorgeous views of big mountains and no worries of drought. Like Western Wyoming or Eastern Idaho for the Tetons.