In some heavy equipment they have something like those as a centrifical pre-filter in severe dust conditions. The spinning thing inside would stop a lot of the dust from entering the main air filter. Although in a heavy equipment with those usually have the engine always running at a constant rpm. Vehicles that vary throttle a lot wouldn't work really well I don't think.
As for the suspension, I think I'd keep it stock than to have it that stiff. He would three wheel over speed bumps at the mall set up like that.