I'm not a big fan of the cutesy names like you mentioned, including Polly. It's fine as a nn but it's just such a little girl's name, you know? I'm always reminded of Polly Pocket though when I hear it so it sounds extra silly to me. nms but not terrible.
Oh, yeah, they make great nns :) But I can't help but feel bad for little Polly if she wants to go into, like law or politics or something. She wouldn't have it as bad as a Rainbow Evening or something but still lol