20 miles is nothing. I've driven 50 miles (each way) to get to a bike store before.
The Trek stores, like everyone else has said, if good if you like Trek/Nike/Bontrager. Basically, its the equivalent of going to the the Trek online store on their website. Prices are nothing spectacular unless you wait til closeout season. The one in SD is selling the SSLx for $5500 or so. Then again, thats probably what they bike should have sold for in the first place.