All my bikes have mudguards, and tyres that can be used all year round. I don't have a collection as such. They are very different from each other and serve different purposes. I don't commute now as I'm retired but I made the effort to ride to work sometimes regularly, sometimes less so over the last few years of work. None of my bikes were new when I bought them, but they clean up well when I get the urge. None of them could be descibed as built for speed. That ship sailed long ago in my case. For a long time I had just one bike which was used for everything all year round.
The last time I bought a new bike was in 2006-7 and though I kept it clean it didn't get used just in the summer. If I was to splurge £1000 plus on a new bike I might treat it differently but that's not likely to happen. All my bikes together are worth a lot less than that! Replacing them would not be difficult but I expect most cyclists are like me and like to change and improve components to get them the way they want, so I'm a bit careful about parking when I'm out. If I'd spent a lot on something really blingy and up to date I'd be afraid of getting it scratched or nicked and in a way, though nice to have, for me it would take away some of the pleasure of owning it.
Still, it all depends what your inclinations are and if you have a shiny speedster that you want to keep as your best bike by all means go for a more "disposable" bike for the winter. The irony is that the winter bike will probably be with you longer as the summer bike might be part of a chain of incremental upgrades over the years. It's nice to have new stuff but there's something to be said for having an "old faithful" bike with a bit of history behind it. Best of both worlds perhaps?