I think the wii fit is quite good for the basic yoga and some of the muscle exercises as I can feel them working. You need your core muscles to be in good shape for good balance etc which is helpful when playing sports. I can work up a good sweat with hula hoop and step so i think you need to tailor your work out for you and just use it on days when you've not done any other exercise.
My exercise plan for days when I've done no exercise in the day but don't want to go out for whatever reason is:
Yoga: Sun salutation, the warrior, the triange, the bridge
Muscles: jack knife challenge, lunges, triceps
Aerobic: beginner jogging, hula hoop x3 and then free step while I'm watching the news
Hope that's helpful.