Joining in very belatedly here...

I think that part of the reason that Elizabeth and Charlotte see things so differently is because of the difference in their fathers.

Mr Bennett is a man of "quick parts". ('Parts' in this sense meaning 'high intellectual ability or cleverness', according to the shorter OED.) Elizabeth is close to her father and shares his intelligence and cleverness. If another seven years passed by without her receiving another offer, I believe she would be more willing to compromise to some extent over what sort of man would make an acceptable husband, but think she would still prefer to be poor than be tied for life to a stupid man - rather like JA herself.

Sir William Lucas is decidedly not the sharpest knife in the box, neither is Mr Collins. Both men have an over-inflated sense of their own importance. Charlotte has had twenty seven years to learn how such a man may be managed into being a tolerable husband, and so would see Mr Collins in a more favourable light than Elizabeth does.