Hello. I guess you could put the balance board on a step (provided that it fit, etc.), but I wouldn't do it. It would be hard to do the side steps, etc. with it up higher off the ground. I would be afraid of tripping. Your score is based on stepping in time as well as doing the step, so it seems like it would be difficult to do it properly if you lifted it up. I would suggest simply lifting your knees higher and just using the balance board as is if you are trying to get more out of your workout.
I like the cardio part of wii fit. You can do step aerobics, boxing, running, or hula hoops. I sweat more in the cardio part than any other part. I love wii fit. You can go longer if you want to burn more calories.
There are about 10 or so exercises in the four sections - yoga, aerobics, strength training, and balance games. Within each exercise, you can make them easier or harder.
I really enjoy it. I am not big on exercise so it is great for me.
I hope that helps.