I think we can all agree that for most of us Wilt's appearance was a major reason we got curious about the show in the first place.
I was watching "Make Believe it or Not" again recently. I always love how when Goo got really sad, Wilt looks over and is like awww she looks so left out and then includes her back into the game.

I think this episode really made me think about Wilt as being well older than the others and can be more like a big brother/parental type.
He just seemed really sweet with the "oh okay.." saying it in a way an adult or older sibling would to humor the kiddies.
E: I know he's not like this
all the time, but in episodes like this you can really see it shine through. :3 That's just how I feel about it though.