THE PILOT REPORTED THAT DURING AN APPROACH TO RUNWAY 30, HE INTENTIONALLY TRIED TO LAND OFF-CENTER TO AVOID A SOFT AREA; HOWEVER, THE AIRPLANE DRIFTED 'UNKNOWINGLY' TO THE LEFT. JUST PRIOR TO TOUCHDOWN, THE AIRPLANE ENCOUNTERED A GUST OR 'EDDY' AND ROLLED LEFT. THE LEFT WING DRAGGED IN TALL GRASS ON A SANDY BANK BESIDE THE RUNWAY. THE AIRPLANE THEN TOUCHED DOWN AND VEERED OFF THE RUNWAY. THE NOSE GEAR COLLAPSED AND DAMAGED THE FIREWALL. THE PILOT STATED THAT THE WIND WAS BLOWING FROM THE WEST AT 17 KNOTS WITH GUSTS TO 21 KNOTS.