Well! I would guess that, for most people, the song would only work without the irony and double irony etc. I would say that for most people, the thing they like about the song is the fact that this once naive girl/women can now see the subject of the song for what he is - vain, shallow and full of himself, and that she can now articulate that for the whole world to hear! Now, how does the ironic version go? He's not vain. He's not full of himself. He's simply a misunderstood chap, and it's the narrator of the song that has lots of issues herself that she needs to resolve.

p.s. It's interesting that George P raised the subject of the ironic " I'm not in love", because Carly did a great version of the similar themed Hoagy Carmichael song " I get along without you very well". And, no! I haven't shot myself in the foot by mentioning this.