Polish to the extent that surface cracks cannot propogate. Further than that I think is no more than an ego trip. I even might suggest that a higly polished inlet tract is of doutful use smooth and direct yes, highly polished? I am not sure. In that regard I seem to recall something about almost stationary boundary layers in fast air flows and also stuff about the dimples on dolphins skin I guess the friction between adjacent air molecules is less than between a solid and air. I guess the same effect applys to liquid to a lesser extent