My wife and I would prefer a ranch-style house as we age, but it's not an absolute requirement. We need 2 true bedrooms, 2 additional offices, and his-and-hers bathrooms, so that takes us to a size where ranch houses can be hard to find, at least in areas where land is expensive. Oops.
When you remark on elevation -- is that (almost) all about flooding, or is it about fog as well?
A lot of areas of California are bad for hill/canyon fires; is that area among them?
I'll look into Rohnert Park and the Guerneville/Forestville area. The latter does look a bit isolated on the map, however.
Gay area sounds good, as it could be an indicator for good restaurants and bad schools. ;)