Well if they really add some visual / themed variety in a single level, then I'm totally fine with lesser worlds. If not, I'd really prefer smaller, but therefore several differently themed worlds. Having more worlds in Yooka-Laylee fashion would be the best thing, that's right
Having DLC (that might include full worlds) does really not bother me now, if I think about it. Just adding new books is probably the best way in any game to add content, since it's just a tiny object filled with fictional worlds and stories and not a full, new, organic level entrance. And I'm eager to get to know more stories by the twisted minds that'll bring us this game... there's much to grasp on! I know, I'm opening a big, fat barrel with this one. But the inside could turn out to be tremendously tasty, believe me.