"I want to buy a classic car and keep my day to day car, my wife doesn't agree. She thinks that because we're retired and do around 4000 miles a year, a good useable classic would cost less to run than two cars and be enjoyable to drive and look after.
I've found a garage that imports Mercedes-Benz models from Japan, they say cars in Japan are very well looked after and have low mileage, the climate means rust is not common either. I've seen a Mercedes-Benz 190E with low mileage. Is there a drawback to buying such a vehicle? What should I be careful about?"
Your question raises quite a lot of points, so I'll do my best to deal with them one by one and offer some advice.
Whether or not you can rely on a classic depends entirely what you're planning to use the car for and what kind of classic you buy. If you're not doing many miles, then in theory you could rely on a classic. But what sort of miles are they? Older cars don't really appreciate very short trips to the shop. Do you have to travel to see family? Or a holiday abroad? In these cases, you might appreciate creature comforts such as air-con and a good radio as well as improve fuel economy that modern engines offfer. And what's the plan if the worst happens? The garage that looks after your modern car may be just a few miles away and able to offer a replacement courtesy car. But which garage will look after your classic? And how will you get about while it's being looked after? These are old cars and you need to budget time and money for TLC.
Classic cars are a great hobby. And if you choose something mechanically simple like a Morris Minor or Triumph Herald, you'll have the added pleasure and satisfaction of being able to tinker with it... if that's what you want to do. There's also an excellent social scene around them. Clubs that cater for MGs and Jaguars (just two examples from) have lots of events and meets you can attend. Will both your wife and you attend? Or will she need a car on days/weekends your away with your classic?
As for importing a car from Japan, it's true these cars are often more rust free. But with a car like the Mercedes 190, which was well rust-proofed to begin with, you really shouldn't have any trouble finding a good one in the UK. Remember, low mileages aren't always a bonus with cars. We've had plenty of old cars that have caused more than their fair share of headaches because they were low-mileage. For example, if it's not been stored correctly, the fuel tank could corrode through lack of use causing rust flakes to gum up the fuel filter or get into the engine and cause problems.
Insurance-wise, you'll find that most classic policies are competitive. This is because many impose mileage restrictions (which shouldn't bother you) but also because they expect you to have another car to do some of the heavy lifting.