You have an interesting point - If SW paid much attention to Anne, she could be a mini Elizabeth! shudder

However she couldn't have developed into the steady woman she is now without some help and guidance - Lady Elliot would have started her off, and LR would have continued that role.

I don't think neglect is her ally, she is the person she is in spite of neglect. Deep down it hurts her:

'Anne always contemplated them [the Miss Musgroves] as some of the happiest creatures of her acquaintance; but still, saved as we all are by some comfortable feeling of superiority from wishing for the possibility of exchange, she would not have given up her own more elegant or cultivated mind for all their enjoyments'

I get the feeling that she'd really like to be as happy as the Miss Musgroves, and puts on this attitude to stop herself from going crazy.

The 'superiority' theme is one I also want to expand on. I'm increasingly convinced that Anne did pick up some of the Elliot snobbery, only of the intellectual kind. Above, she values her own intellect over the social and emotional intellect of the Musgrove sisters. The narrator also puts down Mrs Musgrove's 'large fat sighings', and Mrs Clay's abilities to please. I think this is the ON slipping into Anne's thoughts momentarily (similar to what happens in Emma), and we're seeing that Anne copes with her unhappiness by consoling herself that while her peers may have more attention and love, better relationships, and a happier life, she at least has a better character and mind than them.