I've thought about that, i should probably do more detailed analysis of what the actual cost difference would be. I've looked at Presto as well... but again that is just another tech stack to manage.
the consumption is very SQLish based. "operational toil is higher with Spark" <- I agree with this, this is why I'm leaning towards Redshift. Throwing away half the codebase in favor of some SQL statements is tempting.
Metadata management is becoming a big deal in data engineering these days. It's hard to find good metadata management that doesn't tie you directly into some product or ETL tool. We need more agnostic metadata management tools.