That is the problem with shelters, I've had very few horses that would go in them and I'm sure a lot of that is fear of being trapped in a confined space by other horses that may be bullies. I have a friend who bought a lovely one but several years on and its never been used by her two yet if she leaves their stable doors open they will happily take themselves in to their individual stables and spend the night there!!
If your horse can't get into shelter I would spend the money and buy a couple of blankets with neck covers for wet and snowing weather - always good to have a spare.
Kinda on the matter, even though I do not plan to clip for winter and blanket, I do have a shelter, only 2 horses on the field, however, at the moment I have only seen some poo piles there and they explored it when it was something new. Never caught them in there. Ok, we haven't had bad rain and snow yet (thank god). I have one blanket ready, however it seems to fit the fattest horse, not the one that might actually need it.
They seemed to do fine in the shelter, and I don't they will fight too much there, but sometimes I think they have bad reasoning. Why stand with your tail to the rain or wind instead of hiding under the roof?
I know plenty of horses who get winter turnout through the day for a couple of hours. they just get a waterproof outside blanket, one of them used to get a fleece underneath as he was freshly body clipped, both blankets with a neck piece, and he would hapilly spend his days outside, he actually sometimes got too warm (dark blanket, sun and lots of running). But then they switched his fleece, cooled him off, nice warm stable rug for the night. Never had any probolems :) He had an outdoor box, stable rug with no neck, neck shaved. No problem. Of course, it was not colder than -10°C