With air cooled a major pro has to be less components, vastly easier to manufacture cheaply and easily, easier to work on, but larger due to needing surface area.
The major downside to air cooled is noise, that is why porsche had no option but to go water cooled, as the water jacket kills a lot of the noise of the engine, water cooled can maintain temps more accurately to the desired level.
Just my thoughts.
tabetha