> It's quite easy to get no change with a not-dumb algorithm selecting
coins if you have a decent number of outputs well under the value
you're paying.

I have been playing around quite a lot these lines, too and created some content that is worth to look at: https://github.com/nopara73/ZeroLink/#coin-selection
Also, you can try a simpler privacy oriented coin control implementation with HiddenWallet:  https://medium.com/@nopara73/coin-control-is-must-learn-if-you-care-about-your-privacy-in-bitcoin-33b9a5f224a2