I agree with George's point that balsa's soft surface might cause problems in the area of puncture resistance. Balsa's, "Side hardness load perpendicular to grain," is only 100 pounds as compared to red cedar's 350 pounds. For comparison, douglas fir is 710 pounds, while white ash is 1,320 pounds.(1)

This may be why one hears, primarily, about end-grain balsa being used. One thing to consider, though, is that you may only have to increase the lay-up thickness on the keel and bottom, where punctures are most likely.

One important thing that hasn't been mentioned is that cedar or redwood will undoubtedly make a prettier boat, when finished bright.

(1) The Gougeon Brothers on Boat Construction, A-1