Regarding payback: Solar for southern states makes a lot of sense, with payback in 8-10 years. It makes more sense in California due to high PG&E rates. I have solar (4.25kW system) and it amply covers my needs.
Regarding mooching off non-solar homes: I pay a minimum bill every month ($12-13?) even when my meter is spinning backwards. The net balance is paid out yearly, but not at a retail rate (I wish) but at wholesale rate, which is a pittance. I have produced about 15% more than what I have consumed, apparently a gift to PG&E.
Regarding grid: PG&E implores us to temper our AC usage. They even paid me $50 per AC unit to install a governor to automatically switch it off when their grid load is high. This is reflected in their peak rates period (2pm-8pm). Guess when my solar is producing the most to help out PG&E, and hence my neighbors to enjoy their ACs uninterrupted? Despite higher day usage in summer, I contribute power May-September when it is needed most.
Regarding warranty/repairs: The solar panels are guaranteed by the manufacturer and the installer for 25 years. The inverter is 10 years, I think. I can open an app and look at all the metrics live right now. Something is wrong, I can see it, and SolarCity (Tesla) can also see it. Till now it has just been pressing the reset button couple of times.
Regarding construction: I am in south bay of the bay area. There is lot of dense housing construction everywhere, especially in San Jose, Milpitas and Santa Clara. I would say that easily >10k homes (condos) have been added. It is reflected in traffic, unfortunately.