What does that suggest about beauty (or ugliness) as a character trait?

In most Austen novels we see how the characters who are less
important are also described as "plain" or "not as beautiful" as the characters that serve as
ornamental balances in contrast to the strong personality and psychological traits of the main
female character. The word "plain" is about the equivalent of unattractive and is less used as a
term than "not as pretty". In the "plain" characters we also see flat personalities and
unimpressive characteristics. This can help us conclude that Austen assigned physical beauty to
characters who were most passionate such as Sir Walter and less aesthetic importance to
characters that led the story with their strength and balance such as
Anne.

In Pride and Prejudice, for example, we
see how Elizabeth is "not as pretty as Jane", who is ornamental in comparison to Elizabeth's
strength of character and sense of balance. Yet, the sister with the most flat personality, Mary,
is described as "plain".  

Similarly the Dashwood sisters feature
the pretty Marianne in contrast to the more sensible Elinor in Sense and Sensibility.

Conclusively, Austen allows the reader to create a bond
with those characters described as "attractive" to perhaps enhance the romantic element of the
story, and gives us cues as to the character traits of specifically flat characters by describing
them as "plain".