There is definitely a difference culturally between the east and the west. I grew up in Atlantic City, NJ until I was 23. Then moved to Phoenix, AZ for 15 years. Been in San Diego ever since. People from the east, in general, seem to be more sophisticated culturally and intellectually than those from the west. East Coast people wear more dressy clothes more often. All my friends here dress casually most of the time. People from the west tend to place more value on recreation, fitness, and healthy living. That is merely my perspective and opinion based on my experience and the people whom I've known, but not necessarily fact.
L.A. is more of a big city mentality, while San Diego is usually referred to as being a small town that happens to be a big city- which can be good and bad. The heart of San Diego may now be in Downtown, but the soul is definitely still at the beach and military bases.
You're right. Orange County and L.A. seem switched on 24/7. San Diego shuts down at night and it's quiet in my neighborhood. I like it. It works for me. For the past few weeks, the temperatures have actually been cool - highs only in the '60s. On the cool side for swimming in the ocean, but great for exercising outdoors. September and October will bring the Santa Ana, and it will be in the 80s and 90s.