The Perfect Site...
probably has a house on it already, especially if you live in Northern California.
The increasing occurrence of teardowns is due to the fact that:
1. We haven't built many new roads in the last twenty years, while the number of cars per household (1.9) is now greater than the number of people (1.8).
2. Many of the better sites were built on with summer cottages after the 06 quake>>fire. Although the "cottage framing" many of these older places have doesn't meet modern codes, it is the site, the light, the tranquility and the views that you are really paying for.
3. The lots that are available now were either not buildable without modern engineering and construction technology, or had constraints that still exist, but can be discounted and still have a transaction.
So what do you look for when buying a site? Southern exposure for light, <40% slope for buildability (in Marin, Sonoma and Napa, anyway), rock close to the surface, and all utlities close by.
Know your microclimates--in Sausalito they seem to change from block to block.
Secondarily you, or your architect, needs to clearly understand site coverage and massing (floor area ratio, building heights, shadowing adjacent property) and circulation for cars and people.