Dollar can collapse in different ways. There’s no single answer to your question.
Weak dollar will mean higher prices on imported stuff, such as oil. There’s less income available for housing – prices go down. On the other hand, weak dollar stimulates exports and leads to higher wages and employment in export-oriented industries (you could say that a lot of high-tech in San Diego is export-oriented). Then there’s an issue of interest rates, which may go up or down, and an issue of wealth (where do high-end buyers keep their downpayment savings?)
And, like carlsbadworker says, there will be foreigners coming and bidding on houses. But that should only be a factor in oceanfront areas.
If the dollar weakens because the government starts printing money to stimulate the economy, that will increase wages of groups being stimulated.
I think that the short-term response would be down, long-term there are too many uncertanties.
