Car choices

We are currently on our third year of California ownership.
We also has a BMW 520D Touring from 2011 with 190.000km.
I am thinking about buying a BMW I3S as a company car, we currently get a climate bonus of 6000€ on electric cars and while it is never a good idea for economy to buy new it is the cheapest car I can imagine myself inside. The Tesla m3 is almost double the price and it has to many limitations anyway, ie limited cargo space, no towbar etc etc.
First I thought we would sell the 520D, value at 10.000€ currently, but it is working like a clock. Never a fault (which we can't say about the Cali with its limp mode a glow spiral errors).
But having two normal cars would make our Cali beeing used almost never during winter and maximum once a week during summer. My general idea is that cars should not be left stationary outside because they will start rusting and brakes will fail etc etc. However, we will save some money but not driving it of course.
What is your opinions?

There are lots of factors here. I suspect there is not as much value in the 520 as you would like when traded in agains an i3S.

I think most people need a normal vehicle as well as an electric vehicle unless you want to rent a car for long tours (which isn’t a bad option) or you accept the longer stops to charge on longer tours. However, as you’re keeping the California, I think a Campervan used a couple of times per month for longer range journeys or hauling large items and for camping will keep it running well. The electric car can then be used for the daily commutes, which I’m assuming are shorter, if you’re contemplating the electric car. Without knowing more about how you use vehicles, that’s probably the way I would go.

Personally I would run the Cali as often as possible.
Cars are better driven, than collecting dust.
Do you really need 3 vehicles...?

Thank you for your replies. I ordered the i3s an are selling the 520D.