I've been through the wind farms at Palm Springs CA once and the one just north of West Lafayette multiple times, which are two of the largest in the country if not the world. I've been past smaller ones as well. Some of the turbines weren't spinning but most of them were. The capacity factor for wind is generally 30-40% (meaning, it produces an average of 30-40% of its potential capacity over the course of a year. Eg. a 1 MW turbine produces 0.4*8760 hours = 3504 MWh / year).
That said, unlike solar incentives, wind turbines are incentivized only based on production (NOT when they're developed), so the developers have much more incentive to ensure that they are maintained and kept online. However, wind turbine technicians are the most in-demand job in the country right now, and many of them are in rural areas like the Great Plains so there is probably a shortage of them, which may explain why some of you have noticed when they're not spinning.
However, it is also true that newer turbines have much higher capacity than older ones (ie. the towers are taller and the blades are longer), which is why I can see that constructing newer turbines could be more cost-effective than maintaining existing ones. Sometimes these old turbines get "repowered" with longer blades to increase their capacity, too, though.
As for environmental impact, the amount of birds killed by wind turbines is negligible compared to tall buildings, air pollution, house cats / other predators, and other factors. Countless studies have shown this despite what the conservative media says.
