I get just the right amount of these emails so it's not worth hiring someone for, while still enough to drive me nuts.
I wish there was a support-as-a-service company that had non-outsourced employees (not contractors) and charged per-minute (or 6 minutes) for support, with some fixed cost for training them how to use your app, and handle basic support questions.
And pretty cool startup idea on the small-scale Support aaS thing.
Suggestion: Keep a tally or produce an estimate of what it "costs" you to service the customers who piss you off. Compare it with time lost, work you could have been doing, impact on your mood, etc. There's no simple formula but you could get a basic metric with some imaginative plugging of guesstimates into a spreadsheet.
I wonder if there's a way for you to foster users supporting users? A community forum perhaps? Obviously these can become toxic too, with entitled users spreading rancour. Strong moderation might work, by you and users you elevate to admin status. Sure, forum moderation may take up your time, but it might be simpler than per-user emails (or whatever). Community fora aren't magic bullets, but good examples exist. Just a thought! :)