I resisted the vest thing for the longest time, but I finally broke down and got a (cheap) Eddie Bauer down vest...and I love it. Nice and warm in the center, but maintains range of motion in the arms. It's the perfect amount of warmth for days when base + light fleece + jacket isn't enough, but I don't want to go full Michelin man. Which, in my case, is most days.
I don't get vests. If it's cold enough that you want to insulate your core more, wouldn't you also want to keep your arms, which retain even less heat, warm?