If there was an option to have Claude Opus guide Sonnet I'd use it for most interactions. Doing it manually is a hassle and breaks the flow, so I end up using Opus too often.
This shouldn't be that expensive even for large prompts since input is cheaper due to parallel processing.
That's what I do. I used to use Opus for the dumbest stuff, writing commits and such, but now that' all subagent business that run on Sonnet (or even Haiku sometimes). Same for running tests, executing services, docker etc. All Sonnet subagents. Positive side effect: my Opus allotment lasts a lot longer.
This shouldn't be that expensive even for large prompts since input is cheaper due to parallel processing.