Stiletto is just what happens when you shake the shoe. Both the regular shoe and stiletto are in both SMB and SMB3. I don't know if there is a difference between the shoe and stiletto beyond visuals.
Oh yeah. Yoshi can now interact with objects with which he was never together with before. He can lick fire bars and jet engines and spit out a fireball. They essentially give him an infinite source of ammo for fireballs.
You just made me think of something, what does shaking the Yoshi egg do? We haven't seen that yet, right?