W00t for base layers. I use Craft. Both winter and summer. It's amazing what a base layer with a windstopper front can do. I've used that plus a jersey in weather colder than I thought possible.
It's a quandary for me. Knee warmers don't seem to fit well, but they low bulk. Tights fit better but taking them off mid ride is not looking good. Again, CA is different..if I knew I wouldnt be taking them off is wear tights for sure.