If you are keeping watches for investment, are they remaining in the sealed never opened plastic? If so, I do not think they need to be serviced. If they are being used this is another issue. If you get your watches out of the safety deposit box and wind and set them and play a little then yes they will need to be serviced. As for the California climate I cannot comment as I am from the Midwest but many banks here offer safety deposit areas that are temperature and humidity controlled. This is ideal for storage but if your preferred bank doesn't offer such conditions or you are unsure, buy a cheap digital thermometer with humidity feature.
I got this one at a local hardware store. It is battery powered and will record high and low rates achieved. This allows you to see if the humidity goes up in your safety deposit box on the weekend when they turn their AC off. I use this one in my shop to help monitor the humidity so my tools, parts and watches do not rust. There are also products to absorb moisture that you can put in the box with the watches if the humidity is high. Hope this sheds some light.
TCP