"What I’ve learned (aside from sucking it up, and sending a kind, helpful response) is: design your product as if it was going to be used by people that are a software literacy step below the target user."

Completely with you on the 'sucking up and sending a kind helpful response'. Snark does not pay. It makes no sense to snap at a user.

Regarding the other point about first-time users. I have a slightly related theory.

When you design something, design it for someone who has the attention span of a two-year-old. Not because your app is going to be used by a two-year-old. But because that is how much mental bandwidth a user is going to give you. Your user is probably busy or just likes to multi-task.

Working that much harder on the UI pays off, or at least prevents a disaster.