I personally feel like 4 is good. 4 seasons, 4 festivals (even though they overlap the seasons in some cases).
Although, with how they keep starting Food & Wine earlier, maybe some day they'll push Food & Wine back enough to let it run from July-early September, and then they can have an old-fashioned, New England style Harvest Festival from late September until the Holiday festival starts. (They could serve a variety of ciders, root vegetables, and spiced-pumpkin everything and teach people how to store or preserve their garden bounty.)