For rare cards, could be, especially if you own one, and others report good successes... If buying new, good reasearch would put that extra $40 to work and get more oomph than the overclocked boost from a stock card gives, which it too can overclock good on its stock air cooler..
I often put GPU coolers on high-end cards because it often significantly reduces noise and slightly reduces the temperature of the system. However, if noise is not a big concern I would not recommend an after-market GPU cooler. Plus, if you're serious about overclocking, liquid cooling is the only way to go in my opinion.