I agree with you that Anne's returning bloom is due to more than sunshine, sea air and exercise. I think that the stimulus of new scenes and enjoyable company has a lot to do with it.

I also agree that meeting Benwick, the first new person she has encountered in years who can converse with her at her own intellectual level, has given her the encouraging feeling that life may yet offer romantic possibilities for her. In support of this I note that at her second brief encounter with William Elliot at the inn Anne notices his "agreeable person" and "felt that she should like to know who he was." Also, when Anne is about to leave for Uppercross we have the following:

Captain Benwick was most considerately attentive to her; and, united as they all seemed by the distress of the day, she felt an increasing degree of good-will towards him, and a pleasure even in thinking that it might, perhaps, be the occasion of continuing their acquaintance.

I can't find evidence in the text that hope of Wentworth's returning interest has much to do with restoring Anne's bloom, though a lessening of tension between them has probably helped. Apart from the incidents at Uppercross when he helps her into the gig and lifts little Charles off her back, the first positive sign from him is when he is alerted by William Elliot's admiring glance at her that she is "looking remarkably well".