A couple of sources from the National Trust for Historic Preservation should help. Specifically, the work of Constance Beamont. Look up that organization for two books, "Smart States, Smart Communities," and "How Superstore Sprawl Can Harm Communities."
My recollection of the literature I've read on the topic is that, from a market analysis perspective, most smaller local businesses are adversely affected when WalMart comes to town (dahh...), and I think the economic reasons for that are obvious. What is more important to planners is how to save the downtown businesses; it appears the way for them to stay in business is to find and serve "niche" markets. Small businesses cannot beat the big box at their own games, so they have to do things differently. The alternative, not to allow WalMart in the community at all, has its own problems, of course. Jerry Weitz