Steve - there is a fantastic towing company that services the Pismo dunes. They can - and have - towed people out of the worst situations imaginable (ever seen a Winnebego stuck in 5 feet of ocean water?). However, they do charge a premium.
Personally, I'd rather try to bribe someone with beer. If you want to go the safe route, however, and have the towing company do it, you can reach them (Angello's Towing) at (805) 481-0355. Unless something has changed in the past 12 months, they are the only company that tows on the beach.
The central coast gets very hot in the summer, cold in the winter, and erratic / nice in the spring and summer. I've lived in San Diego through high school and Santa Barbara through college, and can tell you that Santa Barbara gets hotter in the summer months. That said, I never found Pismo to be too cold during spring / fall, and it certainly was not crowded. Like I said before, bring firewood and warm clothes.