I don't think I understand. Why would you "bring online" some wind turbines in a period of high demand? If you already have them, why wouldn't you be running them all the time and use less coal? You're not paying for the wind. Then you still have the problem of spooling something up and down to match demand, but your baseline coal use is lower.
I'm not trying to disagree with you, I just don't get it. Your logic would make sense to me in any other case where there was a fuel cost to the "little generators." Possible holes in my logic include: (a) wear and tear on a turbine in its active state relative to just sitting outside unused might be comparable to the price of coal that is/isn't wasted; (b) something else?