My 2 centimes worth (what's that in euros?):

I've got three mirrors, usually set to "fully off" position to avoid seeing the moron tailgating me in my '83 245 with its enormous rear window lettting in US legal ultra bright blue xenon or whatever you want to call em headlights. This lovely so. Cal. vehicle, now stuck in uncivilized ne OH rustbelt, has now at least 200k mi, god knows how much of the original 105 hp are left even though it burns not a drop of oil. As odo/speedo no longer work i've stopped caring about miles and speed just like when i'm riding my '75 fuji 15 speed bicycle.

Aren't there more important things to be concerned about, you've already got the classiest and safest car on the road, do you really need to show off your louvered backside to the dimwit behind you? Let him admire the fact that you're rolling smoothly, listening to (hopefully) enlightening music/conversation and doing your part in staying out of the buy/lease-a-new-vehicle-every-three-year-madness? Said tailgater is more than likely indebted to the bank for some asian status symbol and is so busy with his palm pilot or porn video on mobile vhs to take any notice of the louvers anyway. He might also be perusing the FinancialTimes to see who's next in line to buy Volvo so the price of your needed louvers might be raised 10 times by the time you're ready to install them.

Yes, times are tough here in the former heartland and an '83 might have to go another 20 years.