I jump there almost exclusively during the week, and there is usually plenty of action. A mix of Tandems and up-jumpers usually keep the Caravan flying, and it is not uncommon for the Otter to be in use.
Give them a call before going over there to be sure.
Skydive San Diego 800.FREE.FALL (In California) 619.216.8416
I drive down from the Los Angeles area and there have been very few times in the last decade that the aircraft were idle. There are of course two very busy DZs to the North of San Diego... Elsinore & Perris...
SDSD is a way cool place. I showed up there all the way from Baltimore a few years ago and they went WAY out of their way to make sure I had everything I needed and I had a good time. People even tok me for dinner after hours. I only regret that I haven't been back.