I can attest to the beauty of visiting/hiking zion in the winter.  No crowds at all.  Cold, but you warm up quickly while hiking.  When I was there in december 2015, the lower emerald pools trail was icy, but passable with care.  The angel's landing hike was hairy (upper part) but gorgeous and well worth the effort.  Less restaurants being open can be alleviated somewhat by buying frozen food at a walmart on the way.  Most hotel rooms in springdale have fridges and microwaves.