I used to be no-hood guy until recently. Like the OP, I wore a hoodless jacket and fleece or wool watchcap. I was always able to stay warm enough.
But I was never cozy.
I've recently switched to using hoods and it's made a world of difference for me. Not only am I actually able to achieve feeling snuggled/cozy like I never quite did with gap between the hood and collar, but I've found that the weight-to-warmth ratio of a hood is much better. It's not just that a hood covers your neck, it's that it funnels all the body heat escaping from your collar up around your head, instead of just, you know, out into the woods.