How to determine when additions are worth it? San Diego, CA

[Madison Lowe]

I own a home in an area San Diego, CA where process are starting to increase. My home currently is valued 365,000. Others in immediate area on same street or 1 street away are valued at 400 or more. My home has been remolded with new roof, 4 bedroom 2 bath, built 1976, 1600sq ft. my home has the same type of home improvements as the others that are higher. I also am on a corner lot. My has an unofficial addition added 20 years ago. I can do some curve appeal but that will not boost my value that much. How to determine how to get my value up to par. Should I try to permit the addition now, the laws probably were different 20 years ago?