This is a difficult one, and I can think of 3 things to consider.
If THINGS stay as they are it will appreciate, the day they stop making them, all Defenders in existence will become a past model which turns the tide and starts a reduction in Defender numbers worldwide (unless someone SOMEWHERE gets the chance to build it for another market - but even countries with the most relaxed safety and emissions laws will catch up with us and they will be no more). This means my Defender, your Defender, the guy down the road's Defender is now technically worth a little more as they are now of limited numbers. However, the issue is, we need to spend so much on them keeping them going, it might not actually work like that.
These aforementioned THINGS are our ability to run an old vehicle; slowly older vehicles are being pushed off the road as a daily driver and in some places even as a weekender. London is an example with its LEZ charge. By September 2014 Parisians will not be allowed to operate cars older than 17 years within the A68 motorway, which doesn't just circle the very centre. Just you wait till the EU decides that that was a jolly good plan and enforce it on every city in the EU!
Next, fuel. I have a daily driver and my 90. I did about 90 miles this morning which according to my MPG average I did on 7.87 litres of fuel at £1.35 a litre, so £10.63 in diesel, when 100mpg is the norm and it costs £2 a litre we will all be moaning, but actually, that would cost less than it did for me today, it would be £9.10. However, if I used my 90 and drive really carefully, it would cost me £29.25 at £2 a litre. I don't expect our salaries to increase enough that it would be on par with today's higher motoring costs for an older car.
MOT and TAX - I suspect they will change this all again sometime in the not too distant future, there were discussions about moving the VED exempt age but it may also come with mileage limitations - I read recently that some places in Europe you can only drive a classic 3000 miles a year. Well, after my rebuild my 1990 land rover is good for another 23 years anyway, but due to the higher build quality, galvanised parts and buckets of Dinitrol in it, I would hope it would last double that with care and attention - but will I be allowed to drive it in 46 years?
In conclusion I think that motoring with older vehicles is going to get more and more difficult unfortunately, what would it do to our Land Rover's if they announced that in 2018 all vehicles over 17 years old were going to be banned from cities, limited to 3000 miles a year, charged high VED for pollution? Well the bottom will fall right out of the market and we will be left with unusable vehicles, which were worth thousands, now worthless. It's not really worth thinking about because the whole prospect angers and disappoints me.