I do keep my winter - summer items together as well. I just don't have an area where I could store the off season stuff, other than the closets themselves.
I do have three closets at the moment:
One is a folding closet. I think this was designed as a pantry but my kitchen cabinetry is quite generous space wise, so I really don't need a pantry. In this closet I hold my knits, sweaters and jeans. What do with this closet is that I switch what goes on the more reachable shelves according to season and either use space bags or the bottom shelves for out of season stuff. Yet, everything is still at eye's view. I do keep my bags here as well on a top shelf and in their respective dust bags. This is the closet that gives me the most headache, especially when I do my Tasmanian devil routines in the morning and I just unfold all of my stuff in haste.
The second is a hanging closet that holds my blazers, shirts, dresses and skirts plus work pants, vests etc. I use items from this closet all year long, therefore nothing gets put away. I do keep most of my shoes, inside their boxes, in this closet as well. That is the area where I could use some improvement, shoe storage, but it always stays nice and neat.
The last closet is our shared outerwear closet. Little Zap and I share this closet.