You're not on the coastal strip. Sorry. We live in San Mateo, don't have A/C and we really don't need the heater but for a month or two, and even then rarely all day. Older houses typically are more comfortable around here without much effort, except maybe a little insulation in the ceiling and a reflective roof positioned to deflect summer sun. Modern California houses are over-insulated and lack ventilation, as dictated per the nanny state. Thus making central air and heat absolutely necessary no matter what the outside climate is.
I was in Palo Alto--down the road from San Mateo--on September 6. That afternoon, it was pretty hot, and you might have benefited from air conditioning.