I lived in Coronado during the last crunch. My mom, in a rent-to-own snafu, bought the cheapest house on the island at the time. 289 in 1990. Coronado does go down, it just does so last. Hazarding a guess as to how much though is a fools game for an individual zip code.
Coronado in particular used to have a lot of senior navy officers who lived there. They have been chased out by the prices though. I suspect much like everywhere else, its a much more transient place than it was last time around.
Rats, there are no rats in Coronado! Next thing someone will say is termites in Del Mar!