One comment: the biggest favor you can do yourself if you want to do solar is to reduce your energy consumption. The less energy you use, the easier/less costly a solar system will be (or, the more power you can sell to the grid!) You cannot sustainably be on solar unless you have good energy habits.
Worst power utilization offenders include baseboard heaters (forget it), dryers, electric furnaces. Step one of any solar project should be an energy audit.
After I in installed my system I replaced every incandescent bulb with LED and increased my excess production significantly. The credit I get from my utility (grid tied) is fairly low, but hopefully we will be able to sell or donate our excess by the end of 2018.
I agree that it's helpful, but I don't think it's necessary. The price has come down so much that a lot of people are just switching without making any adjustments to their energy usage. Ultimately this is a good thing because it's otherwise natural gas for those energy hogging appliances, and I'm all for being done with that mess as well.
I guess it depends what we're talking about. If you are talking about a grid tie system, where any power you generate goes back to the grid, you're absolutely right. In that case your energy use and the power you sell to the grid are independent and have nothing to do with one another.
If, on the other hand, you are talking about an off grid system, energy utilization matters very much, as you'll need a battery bank large enough to sustain you, and you'll need a PV array large enough to recharge that battery bank in a reasonable amount of time. In this case, every bit of energy matters. The difference between someone who reduces their energy and someone who maintains their standard power utilization profile would be in the tens to hundreds of thousand of dollars.
Certainly the cost of batteries makes a big difference, but that cost will be coming down pretty drastically in the very near future. It's hard to imagine going into hundreds of thousands though.