I think part of Susan Boyle's charm is that she doesn't "look the part" or "act the part", yet she has the resilience and confidence to just keep on singing.
We keep talking about her looks, but remember, she's also 47 (I think. ??) and looks 47. Not exactly your TV-talent show ingenue. And, as much as we criticize for looks, I think a big part of it is age as well.
She's middle aged, and that means smack in the middle of being "young enough" to look good even if you really aren't very pretty (Now that I'm middle-aged, I realize every single 20 year old in the world is gorgeous! LOL), nor "old enough" to rely on character and wisdom and fortitude. If she'd been 77, the audience would have been much nicer, perhaps even being on her side from the beginning--we love plucky Senior citizens.
I think it's great that Susan is making us rethink some of our "first impressions" and steretypes, and that's always a good thing.
But, like many others, I think she's making us rethink giving up our dreams due to "the odds" and that is an even more important message.