We are both playing with numbers – we all are. There are a million variables, so we have to make assumptions based off the data we have.

What is the percentage of parents who help their children with the DP on their first home?

According to the statistics you provided, there are nearly 450,000 people aged 20-29 in SD.

According to PayScale the median salary by age for SD is $63,733 (25-44) and $41,884 (18-25). San Diego is one of the highest cities in the nation in regards to % of college graduates – over 40%.

Top 10 college majors (average starting salary) as of March 11th 2008:

http://education-portal.com/articles/Top_10_Paying_College_Majors.html

Of those 450,000 people – what % of them need to be in a position to buy and/or save for a DP to be significant in your opinion?

Depending on what you consider to be a significant amount, I may or may not be able to make a strong case.

(And yes, I know a large portion already own. Each year there are also new fish in the water.)