I know this is a year old but I have found a method of movement which I believe is faster than the wheel. It is hard to explain so here is a quick demo:
http://fast.filespace.org/crazychimp132/Kirby_Ninja.zip
Generally, if you fly in the middle of a ninja kick, and don't press left or right, you retain all speed from the ninja kick but don't go down anymore. You then can fly very fast to the side you kicked to, losing speed gradually until it becomes necessary to blow out air and ninja kick again. The ninja kick is actually quite fast moving to the side so doing this efficiently is very comparable to the speed of the wheel, faster in many cases because it avoids collisons with enemies. Generally the strategy should be to kick, get as high as possible flying, kick for as long as possible (since the kick is always at max speed and flying slowly loses speed) and then fly back up, and repeat this for the whole level. Also, it can be timed right so that when you strike an enemy with the ninja kick you do not bounce backward and up, but instead change immediately to the flying sprite after collision and keep the speed. This can be used to get past enemies blocking the way.
This method takes a lot of planning, more than the wheel, but I believe it can be worth it. In some cases it is possible to fly over most of the level. This would of course be better for a single player game, since the ninja's attack can't compare to the power of wheel rider star.
Edit: fixed link