IMHO it is always worth the visit, especially if you already plan on being at WDW while this is happening..
In addition to the lavish gardens and topiary displays (which in itself can be quite a sight and great for pictures), there also special food offerings that are only available during the festival (kiosks similar to F&W), a live concert series at American Gardens Theater (same venue used for CP during the holidays), and it is also one of the few times that the old Wonders of Life pavilion is open and is used as the venue for the "Festival Center" filled with special festival merchandise, exhibits, and seminars..