Some thoughts from my family, not necessarily new stores but augmentations of current ones, too:
*Period clothing, probably its own store. Everything from hats to shoes, underpinnings to overcoats.
*Period toys, to replace the WallyChina stuff across the board. About half of the stuff curently in the Toy Store needs to go.
*Reintroduce the blackpowder guns to the Outfitters. I had actually planned a purchase there, only to find out they had dropped the line.
*Augment the trian stuff at the Depot. Here's one idea: LGB makes a G scale loco that is durn near identical to a couple of the Silver Dollar Line engines. Partner with LGB to package one with a couple revised, old-time passenger cars, throw in an engineer, conductor, and two Bolin figures, a power pack, and a circle of track, and these outfits WILL fly out the door, especially around OTC.