As for types, I'd guess:
Niles: INFJ (I really don't see the P at all, and he's too whimpy for a T ) <3 Niles! David Hyde Pierce is an amazing actor! Shame he's gay... And old... And taken...
Martin: Always struck me as an SJ - very traditional. I'd guess ESTJ
Lilith: ENTJ. No doubt :P
Daphne: xSFx, I'm not really too sure to be honest.
And yes, there are such things as INTPs who overuse emoticons
I love this series too, my favourite episode has to be on in the hospital which I think finishes with them passing rooms in which future selves are having kids and stuff like that, I dont quite remember it but it sticks in the mind.
Got to be honest that it was a show I began watching having watched Cheers and then wound up liking better than Cheers and I empathise with the characters a great deal, unrequited love and being single and having relatives move in and live.