One more point...when you buy "wind generated" power, the power you get probably won't be actually be made by a wind generator(turbine) unless you're real close to the wind farm. Even then it's a variable supply depending on...well...the wind.
What you are buying is wind generated power to be slipped into the grid to replace some power that now won't be fossil fuel generated.
You're still doing a good thing, it's just globally or at least regionally rather than locally.