I understand what you are saying (but disagree about Shrek). Under your logic though, there should be no Best Picture award given some years.
I wish animated films could compete on the level with live action films, but the truth is one would never win. Actors and industry people want to vote for their peers and not animated characters (if that makes sense). By creating the extra category, more animated films get the same kind of respect and promotion as live action films and that's really what the Oscars are all about. Not best anything, really. It's all about PR. Not that it's bad.
On the PR front, I think Ice Age will win. Many people loved the teasers and voters who have kids will have seen it a million times before the votes are cast. It was clever enough for the adults while being very kid-friendly. Lilo was marketed to a kids only audience. That will probably hurt its chances, but it's the second contender. Spirit the Stallion seemed so incredibly dull from the ads. I remember getting restless just watching the trailer, but I don't particularly care for horses. The acadamy could choose this safe choice and the Dreamworks trio has pull with the academy so it ties with Lilo IMHO. Spirited Away is really the dark horse here. Just the fact that it stands out as something different could intrigue voters. And if voting is split between all the other contestants this may pull in Sprited Away's favor. Treasure Plannet has been getting bad press (even by the folks at Disney), so I don't know if it will be a contender.
Just the way I see it. I could be wrong.