Do you have all the iballets? I find I can cycle through all of them in about six weeks doing a couple a week, and not get bored.
That being said, you don't want to overdo any one type of workout lest it start becoming less effective as you get used to it. Maybe work up some rotations where you use them for six weeks and then let them sit for a couple weeks.
Or, make them harder. Sometimes if I'm feeling really masochistic I will use a medicine ball in place of a playball for iballets or a weighted belt for standing work. That'll burn.