Hey, @Amit M. thanks for your question. In Alameda specifically, the ADU or extra units are very normal and in many cases ideal. There are many young buyers who want to have their parents stay with them long term and are open to house hacking to offset the PITI. There is another fairly large segment of young parents with busy schedules who want an au pair suite (likely not renters though). So for that buyer segment, an official ADU isn't necessarily required but a suite with a separate entrance on a different level is ideal.
Generally, you will also find that having three bedrooms on a single level is an ideal floorplan, particularly for families with multiple children who want to live in it as a single family home.
I have found that even many high-end homes have ADUs or au pair suites that people like to rent to traveling nurses, professors on sabbatical, grad students, their kids who come back from college or aging parents (likely no rent in that scenario). That said, true multi-family units or homes with ADUs don't sell for as high of $/sqft compared to true single family homes for a variety of reasons. Rent control and privacy being two. If your goal is to rent and be flexible, I'd go with an ADU that has an internal staircase that can be closed off. If you want to get top dollar per sqft, maybe a 4/2 is better, but that is really neighborhood dependent.
I hope this answers your question.