Thanks for the tip. Looks interesting, but still on the "analyze and do something" side vs monitoring then making suggestions.
In other words, this could be another input for the kind of tool I'm thinking of.
Kind of surprised this doesn't exist, as it seems doable. Given a combination of query optimizers, slow query monitoring, and common tuning techniques, even a rudimentary, heuristics-based recommendation tool could provide significantly more value then manually analyzing explain and log file output.
Looks like there is a service similar to what you asked for, but it only applies to MySQL, PerconaDB, and MariaDB right now [0]. Maybe as PostgreSQL grows in popularity more services will target it. Or go build your own, it sounds like a viable business.
Seems a much more efficient approach than analyzing and diagramming (sometimes) complex explain results.