I do believe that we need more Yoshi, but, honestly, I think I'd rather see another game where you can ride him versus just playing as him, but that's mostly because I want them to get rid of his fat more than anything else. < <;
I suppose a Yoshi's Island style game would be great, especially if it's got all the detail and gameplay of the original game. I'm not entirely sure about a 3D game, though. Even with Wiimote targeting, that could still be a little awkward. But I think they could pull off a side-scroller with 3D elements. Especially if they bring back the vehicles.
Imagine flying over the island with the Yoshicopter. Like, over the whole island.
That would be pretty awesome.