]The questions remains, then: Why do they go to lengths to pretend to be friends with her? My guess is that she, though not exactly to their taste, is better than anyone else to befriend in the country, and if they don't associate with some people, they will be seen as complete snobs. Thoughts?

I agree, and I'd even go a step further. Miss Bingley in particular, being single, probably concentrates first and foremost on finding a rich, socially suitable husband. But when she sees what a confined area her brother has settled in, she has to befriend someone in order to escape boredom. I can only assume that there are times when Mrs. Hurst would be with her husband and Miss Bingley would feel like the proverbial third wheel.

But I also think that Miss Bingley probably thinks she'll look better in the eyes of others for "making friends with the locals", who are obviously beneath her in social standing. When Mr. Darcy, in particular, sees the Bennet girls alongside Miss Bingley, he must see how superior she is...is it possible she's thought it out this far?