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This surprised me - a dog that wins Best in Show at the Westminster Dog Show doesn't increase the number of new registrations for that breed - for at least five years.
For breeds that had won the Westminster Show, the slope of the curve for number of new registrations per year for the 5 years prior to winning was not significantly different from the slope of the curve for the 5 years after winning. Annual percentage change in number of new registrations for the breed that won each year was not significantly different from annual percentage change in number of new registrations for matched non-winning breeds.
Herzon, H.A. & Elias, S.M. 2004. Effects of winning the Westminster Kennel Club Dog Show on breed popularity. Journal of the American Veterinary Medical Association. 225(3):365-367.
http://avmajournals.avma.org/doi/abs/10.2460/javma.2004.225.365
In terms of consumer psychology, winners usually lead to increased sales - but not in this case. I think there could be a few reasons for this:
1. More people are aware of homeless pets and their need for good homes - therefore, less people are buying purebred dogs. However, I don't think purebred dog registrations as a whole have decreased.
2. It can't be related to how many people watch the Westminster Kennel Club Dog Show, because it has increased in viewership with time, especially due to its increased coverage on television and the Internet.
3. People may have their favorite dog breeds, and they stick with those breeds, regardless of what breed wins best in show.
4. There are increased sales of the breed that wins best in show, but people are buying them from non-registered stock. The study looked at the number of registrations, not the number of sales.
5. People that own show dogs specialize in a certain breed, and they stay with that breed through the course of their career.
6. There is little consumer interest who wins Best in Show - that dog does not exert enough consumer influence to increase breed sales.
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