Gramado is quite special this time of year with the center of town well decorated and the hortensias everywhere (as they always are). I have never been there without my spouse. Two of our best friends are spending Christmas and new years there this year, as they've done before, and they do not tire of it. Their seasonal promotion is here:
http://www.natalluzdegramado.com.br/...uz-gramado.php
Bento Gonçalves has lots of interesting wineries and quite a few nice activities also, a short drive away.
http://bentogoncalves.com.br/