Many 911 drivers drop the drivers side window an inch, to prevent the interior steaming up. Rain X anti steam treatment might help, but don't count too much on it.
The aforementioned wheel arch liners by Dominic at SVP (specialist Vehicle preparations, Worcs) might help, as well as the "lokari" wheel arch liners which are used in the Nordic countries. It is a bit of a hassle to fit due to the front oil cooler but hey ho.
In my experience, before I restored my car I went everywhere in it, in every weather. Good winter tyres on either fuchs wheels nicely coated with vaseline, or a spare set of wheels, is an essential.
You have the traction, (weight of engine at back), good grip and better predictability as such with winter tyres. I run my 924S on conti's, my various 911 on michelin but Nick Moss had good experience with other brands.
I would ALWAYS buy a car with higher mileage due to long commutes -appropriately maintained, No cost cutting/corners cut in maintenance- than a low mileage concours queen which needs basically every rubber, seal and electrical component going through. In Amsterdam, at Porsche Club NL, there is a 3.2 with 625 000 km that only now needs a top end rebuild. Fastidiously maintained, driven hard when warm and not moddlycuddled. I have seen inner london cars with 51000 miles with more wear on the seats than that thing.
Once your bottom lines are established with regards to the fluids, filters, brakes, tyres, suspension, bushes, gear linkage mechanism, heating flappers and cables, alternator, fan belts, heating blowers under the dashboard and engine compartment, and all the potential rust spots of the car appropriately treated and waxoiled until kingdom come etc etc, you'd find yourself with a car that hardly depreciates, costs relatively peanuts to run (my wife's Golf is dearer to run) and is the envy of a lot of the drivers in their silver blobs on an expensive lease/HP/PCP.
HTH,
Bert