Another MN barefooter! Welcome!
Here's my take on "having to start over every spring." I used to worry about that a lot more when I was foolishly trying to somehow pound my feet into being tougher. My own personal running breakthrough didn't come until I stopped doing that and worked on running barefoot as gently as possible. Rather than gritting my teeth and suffering through blisters, bruises and stinging feet I heeded that extreme sensitivity and focused on quickly, lightly lifting my feet off the ground. No pushing off and no "striking" or "landing." Just focusing on lift.
In fact, I leverage the "toughness" lost over the winter to help re-center my form in the spring. I go unshod as much as possible March/April and really work on making sure I'm running in a way that doesn't hurt my tender feet. The dividends that pays for helping keep my form light, quick and efficient are well worth it.
Over the last several years I do think my feet have gotten tougher but I don't at all rely on that for barefoot. Instead, the real benefit of barefoot for me has been letting my super sensitive feet instruct my movement.
As for winter running I bought a pair of Luna Tabu split-toe booties and run in huarache sandals even down to about 0 degrees. Use 72" laces coiled up around the ankles with a pair of windbreaker pants and you can be nicely sealed up:
https://i.imgur.com/WvOuQEI.jpg