I'll have to think about it...

Meanwhile, there are seven other references to fashion in P&P (yes, I looked them up ;-):

1) [Bingley's] sisters were fine women, with an air of decided fashion. His brother-in-law, Mr. Hurst, merely looked the gentleman. (ch.3)

(This one seems a little odd compared to the line you quoted...)

2) [Darcy] had seen a collection of people in whom there was little beauty and no fashion. (ch.4)

3) "What an agreeable man Sir William is, Mr. Bingley -- is not he? so much the man of fashion! so genteel and so easy! -- He has always something to say to everyone." (ch.9)

4) The first part of Mrs. Gardiner's business on her arrival was to distribute her presents and describe the newest fashions. (ch.25)

5) Mrs. Bennet was doubly engaged, on one hand collecting an account of the present fashions from Jane... (ch.39)

6) "In [Elizabeth's] air altogether there is a self-sufficiency without fashion, which is intolerable." (ch.45)

7) "But slyness seems the fashion." (ch.52)

Numbers 4 and 5, with an "s", are definitely about clothes, and Aunt Gardiner's use of the word in #7 also seems to mean what it does today, but the others are a little harder to decipher.