I actually don't think the suits are very useful in World 8, W6 and W7 have some levels with a few instances where they come in handy. Saving a Frog Suit is actually a better idea because you can use it to swim under the entire ship that floats in what looks like mud, I think it is the second stage. Other than that you can take out Bowser with a few hammers none of the suits make the levels in 8 easier or more interesting.
Turning into a statue with the Tanooki Suit and landing on an enemy is the strongest attack in the game. You can take out spinies and ghosts and even fireballs. Of course, if you attack a fireball you're going to fall into the lava, but still, you can do it. But there are no levels which play to this strength.