Interesting tradeoff. It's a tradeoff because the bumpy stuff delays flow separation by triggering turbulence, which increases drag over that caused by laminar flow. So you'd probably get a slightly more forgiving sail with slightly more drag.
However, the already bumpy bits of most sails (especially the transition from mast to sail) can be expected to cause turbulence for all but the most boring windspeeds anyway, with the result that the difference between bumped-up sails and regular ones would probably be very hard to measure. It would be interesting to see some results, though.
