+1 to the idea of atomic updates and treating all core smart contracts as essentially a single application with single version.
My suggestion would be to establish predefined schedule for release frequency. So for example, we can decide to have quarterly releases or 6 month releases, but most important part being that it is predefined and predictable.
Without predefined schedule, some changes will always be too small to warrant running through the release process, and it can lead to accumulation of ton of tiny changes, until a huge important change actually needs to go out. This can lead to more difficult upgrade process and also more potential bugs.
Predefined frequency will probably fit well with overall review/audit/governance cycles too. Also it should work better for external contributors, without predefined schedule it can be hard to prioritize making contributions since you never know when your small change will actually get deployed in mainnet.