There is no one place that is the center of everything.
You have activities at the speedway (vendors, demo rides, vendors and races).
Then there is Beach Street (vendors and one of the Harley shops). Also also has Harley Davidson as a display vendor there.
Main Street (across the river from Beach Street (mainly Bars and vendors)
Destination Daytona (actually in Ormand Beach area) US1 and I95 (Bruce Rossmeyer HD, multiple vendors)
Several miles east of Destination Daytona on US1 there are Vendors and several outdoor bars, Like Iron Horse Saloon.
Then there is the cabbage patch in Samsula, just south of Daytona.
Swap meet at Volusia County fair grounds (New York Avenue in Deland) West of Daytona,
I'm sure I'm missing some, but it's best to get a map when you get there of areas and events.
2010 FLTRX Black Denim
2007 FLSTN Vivid Black