Well I've done 7 flushes and try follow a strict no white-food diet (sugar, white flour, rice, pasta). While it has helped in other areas, it has done squat for my sinuses. That's not to say it may help some.
Some sinuses are built different than others. Little pockets, boney obstructions, deviated septums, etc., are major contributing factors to sinus infections - especially deep inside the head. Diet isn't going to help alleviate these anatomical trouble spots.