CA currently does not have an estate tax so there is no CA requirement although there is/was legislation to start. https://sd11.senate.ca.gov/news/20190326-senator-wiener-introduces-california-estate-tax-proposal-fund-programs-reducing-wealth
Some recommend filing the 706 for portability reasons…….being able to
use a spouse’s unused exemption.
Whether that is useful to you or not depends on your personal circumstances. Seems like valuation for step up cost basis could be documented in other ways.