I am from that area, lived in Vallejo and Napa for years. No one will be able to tell you what the future holds for sure, anything can happen naturally. That being said here is my 2 cents worth....
1. Just doing the simple math..., look at the demographics for any large metro area for growth in the last 100 years. All have grown by leaps and bounds it would seem. Growth is inevitable in area that are mobile and offer an abundance of jobs.
2. The Bay Area has a thriving economy. Do you think builders will go out of business and look for other jobs? No way ray. They know that people keep having babies and immigrants continue to flood in.... everyone needs a place to live being second only to food.
3. Can there be a downturn or further lowering of home prices? Yes, it can happen. But.... do you see a lowering of gas prices or milk? When the actual cost of living keeps raising, inflation is inevitable just like death and taxes, you will see that the cost of homes will raise too...IMHO.
Just my 2 cents worth..., good hunting and remember to get yourself a Free Buyers Agent. It should not cost you a dime to hire a Licensed Real Estate Agent in your area to help you through the process.