As Few As Possible.  The following evidence is from Kennedy Smith, former director of the National Main Street Center and CoolTown Studios associate partner:

“I’ve been surveying the main street management organizations in hot (or cool) historic commercial districts over the past few days to find out what percentage of retail businesses are national retailers. Here’s what I’ve found:“

Manayunk (Philadelphia): 5%
South Street (Philadelphia): 12%
Chestnut Hill (Philadelphia): 15%
Allston Village (Boston): 10%
Jamaica-Plain (Boston): 10%
Provincetown, Massachusetts: 5%
Old Town Alexandria, Virginia: 10%
Carytown (Richmond): 10%
Shockoe Slip/Shockoe Valley (Richmond): 10%
Downtown Portland, Maine: 5%
Old Port District, Portland, Maine: 5%
14th + U Streets, NW (Washington): 10%
Dupont Circle (Washington): 15%
Lincoln Road (Miami): 20%
Dilworth/Queens Road (Charlotte): 25%