I think Anne is valued by a great many people within her confined circle. Just not her father and eldest sister.

At Kellynch and its village, I have the impression that Anne is respected and well liked by the staff of the house and by the inhabitants of the village. While Elizabeth can only think of cutting back on charity when the need arises to retrench, Anne is the one who bids adieu to all the neighbours. As she tells Mary on arrival at Uppercross in ch. 5,

"And one thing I have had to do, Mary, of a more trying nature: going to almost every house in the parish, as a sort of take-leave. I was told that they wished it; but all these things took up a great deal of time."

I also think she is valued by Mary, Charles and all the Musgroves, in their own way. They confide in her because she is a sympathetic listener, gives sound advice, does not gossip, and treats everyone with respect. Now we may argue that she is letting herself be used as a doormat and that she has resigned herself to living her life as the spinster aunt, but she goes frequently to Uppercross and everyone appears truly happy to see her when she arrives and to have her in their company, including Mary's young boys.

Enter CW. Anne is reduced to this miserable state of behaving like a mouse [there I go again :-)] and not being able to show her true admirable character.

Finally at Lyme, hardened after several weeks of CW's presence (ie, no longer reduced to silent anguish at the mere sight of him), she starts to behave more like her normal self in the company of CW. "A very good impulse of her nature" indicates to me that it was her usual behaviour to draw people out with kindness and to be truly interested in them.

I agree that this is Anne's turning point in the book, but IMHO
she is merely reverting to how she has always been apart from the aberration at Uppercross. It is a turning point for CW, who finally begins to see the real Anne emerge.