This is pretty much my impression of Lady Middleton.
In many ways she appears a surprising wife for Sir John, being so cool and reserved in temperment.
I agree, we don't hear of Lady M being interested in anything outside her own sphere- only her four noisy children stirred some life into her and she spoils them alot.
She is not disdainful of others nor rude but the word 'disinterested' comes to mind.
The interests of the Dashwood ladies- music or poetry- are as vague to her as they are to her husband. Yet, he enjoys their company.
I find it of interest JA used the term 'insipidity' to describe Lady Middleton.
I doubt she minds the parties either so long as they're conducted with style and she dislikes raillery- outwardly elegant appearances seem important to her.
I think she'd be a suitable hostess to arrange parties - with Sir John providing warmth of hospitality to guests.