The tautology is in only looking at the subset of spending that's done through incentives, and then complaining that it disproportionately goes to people buying expensive stuff. That's what incentive means in this context: incentive to buy expensive stuff.

Anyway, you're coming at this all wrong. If I was in charge of designing this program, my mandate would not be to help poor people or rich people, it would be to increase solar power. How do you increase solar power? By paying for part of it. Who benefits? Whoever's buying it. Who pays to install solar power? Not poor people.

Or here's another way to look at it: What's the whole point of having a solar power incentive? To get more solar power. Now suppose we changed the law governing solar power incentives to exclude rich people (or tall people, or right-handed people, or any group of people). What would happen? Less solar power.

That might be a desirable outcome, if you are more opposed to rich people getting tax breaks than you are to fossil fuels. But in that case, why not just raise taxes on rich people, and leave the solar incentive out of this?