You refer to the '1,000 rooftop' minimum for neighbourhood retail. I expect, by the way, that you were just wanting to position that rule of thumb as a rule which, in isolation, might risk limiting of 'hope' and the will to risk and build. And you've used Seaside as a case study, and so will I. By the way, anything I say here should pass a self-evident common sense test by any of you reading this.
Seaside manifests four additional 'rules of thumb', which in my opinion should generally be included with the first about minimum rooftops within a neighbourhood. (By the way, the minimum perceived in Oz here is 800 or so, but in combination with what I'm about to say.)
First Additional Rule of Thumb: Through Traffic
Seaside has 'through traffic' as well as 'to traffic' passing right beside its retail centre. This obviously increases passing retail activity beyond the number of rooftops within its walking catchment (which is only about half what it could be because half its catchment is the sea).
Second Additional Rule of Thumb: Destination
An urban centre will flourish better from a retail standpoint when it is a destination for visitors beyond its own retail walking catchment of rooftops. Obviously, Seaside is a destination because of the beach and because of its architecture and urbanism (not to mention all the publicity).
Third Additional Rule of Thumb: Focused Urban Structure
Seaside obviously is well structured to focus its retail right at the focus of all its passing trade and destination.
Fourth Additional Rule of Thumb:
Co-location of Retail with Other Destinations/Uses
Retail will flourish better if it co-locates with other destinations, so that patrons with other errands will happen by the retail and use it. For a neighbourhood, that might include a childcare centre, post office (maybe within the corner store), neighbourhood park or other natural amenity, perhaps a 'Third Place', and a concentration of home-based businesses nearby. So "hope" might and should always participate in town-making, but being well-informed should be in there, too.
Note: This post is part of an extended BlogOff on the viability of neighborhood retail. The most recent posts from BlogOff participants are as follows:
12/21 - The Necessity of Hope, Steve Mouzon
12/23 - Retail: When it bends the rules and breaks the law, Hazel Borys
12/28 - BlogOff: Neighborhood Retail, Sandy Sorlien
1/5 - Retail BlogOff, Patrick Kennedy
1/11 - When shops and services are within walking distance, we walk more and drive less, Kaid Benfield
1/29 - Neighborhood Retail Dynamics, John Olson