Okay, so that's good to know (about being willing to move somewhere new). The risk with the type of maneuver you're proposing is that if prices keep going up, you risk being priced entirely out of the market. If all your friends and family are in San Diego, that's a more worrying risk than if the worst case is that you simply start over somewhere new.
Now the second concern is that, even if San Diego property prices are overheated right now, there is no guarantee they'll crash anytime in the near future, and if they crash, it may not be all the way back down to levels which make buying rental property attractive on a cash flow (rather than price appreciation) basis.
I don't know as much about your local property markets, but I know a bit more about the Bay Area up the coast from you.
People thought prices were already spiking into a bubble before the 2000 tech crash, but even the stock market crash didn't slow the risk of property values. The 2008 crash did have an impact on housing prices, but not as big of one as many people were expecting, and if anyone was waiting around for prices to fall back down to something reasonable, they missed their chance to buy at "less crazy" prices before another crazy round of price appreciation kicked back in.
In your shoes I would be worried about trying to time both the top and the bottom of a future pullback in SD prices, because real estate markets have been behaving in seemingly irrational ways in California for as long as I can remember. Especially with the money from the sale sitting in cash losing value to inflation (call that $7,500/year at 3% inflation with a quarter million dollars in the bank), and effectively an extra $10,000 in living expenses each year you wait for the crash to come (with the risk the rents continue to increase if the markets continue to go up instead of down).
But then again the worst case scenario here is probably just that you spend a few years waiting for the crash at $17,500/year, it doesn't come and you end up living somewhere else where the equity you free up from selling your SD condo might come close to buying a multifamily unit free and clear. In the end it just boils down to your risk tolerance.