Is Cave of the Winds worth doing if I've already seen Niagara Falls from above?

Yes. Seeing the falls from above gives you the panorama, but Cave of the Winds puts you in the action at the base of Bridal Veil Falls. You feel the full force of the water and get drenched on the Hurricane Deck. It’s a completely different experience—worth the extra ticket unless you hate being wet or have mobility issues.