McMahon and Austen

Is unhappiness associated with characters that are uniquely perceptive, or happiness with those whom are portrayed as unskeptical or credulous?

Marquise de Chatlet, confessed in her own Discourse on Happiness, to be happy "one must be susceptible to illusions, for is to illusions that we owe the majority of our pleasures. unhappy is the one who has lost them."
-Pg. 202 McMahon

Elizabeth took up some needlework, and was sufficiently amused in attending to what passed between Darcy and his companion. The perpetual commendations of the lady wither on his hand-writing, or on the evenness of his lines, or on the length of his letter, with the perfect unconcern with which her praises were received, formed a curious dialogue , and was exactly in unison with her opinion of each.
-Pg. 83 Pride and Prejudice

     Elizabeth, who's judge of character we've come to trust, thinks about how "exactly in unison" the conversation proceeds with her "opinion of each". She is distrustful of the superficially gracious Miss Bingley and observes Darcy to be keen and brooding. At this point in the story  Miss Bingley is making exceedingly superficial repetitive observations of Darcy's writing process. Her dialogue is marked with glad/excited explanations throughout. It seems to wear a facade of happiness. On the other hand, Dacy's responses are dry and witty, if he responds at all. He does not seem to express happiness near as much as any of the other characters, throughout the story, but constantly demonstrates his sharp perceptive abilities. It seems that unhappiness in him is associated with a certain "loss of illusion". Furthermore, when we analyze the character of Jane we observe a character that is portrayed as eternally pleasant and happy yet fails to possess any ability to perceive a deeper nature in others, past their unanimous good intentions.