That won't cause any land depreciation or decrease in the value of the land. It may reduce the sale price, if concrete block has no value to a purchaser, but only by the amount that it would take to remove the concrete block. And if the land is so valueless that concrete removal significantly impacts pricing, the land wouldn't have been valuable enough to instal wind turbines in the first place!

So this sort of FUD seems to be extremely weak. Wind power is a massively profitable business, the amount of money that can be made dwarfs the capital costs of the construction, which in turn dwarfs the cost decommissioning of non-toxic materials.