I'll add my recommendation for good lighting, and for there to be a wide range of fabric types. It can be very discouraging to find that a store is only reproduction fabric, or that another is entirely devoted to 15$ a yard Amy Butler or something. A girl likes a little variety in her prices and choices, you know?
Also, if you could have sewing machines on display I always love to see that, especially if you pick up a neglected treadle or something and give it a good home. It wouldn't be too hard to install a lock or to just remove the needle, but I know there are folks who would love to have the chance just to mess around on an antique!
A wide variety of rulers are always a godsend--I hate seeing only one brand, if you just have maybe one or two of a couple brands of rulers it would help me decide which one I would want.