Definitely reflective sidewalls are at least as good. No disagreement there, and in Michigan they specifically list reflective sidewalls as an acceptable alternative to spoke reflectors in the law.

Tires with reflective sidewalls are in the minority however. I will be mounting my new Marathon Winters in a few weeks when the snow comes, and I might decide to lose the reflectors for the winter at that point. But it's hardly worth it for weight/time purposes - I'm a total overweight slug all winter. And reducing the dorkiness of my ride is like taking a cup of water out of the ocean.