Non compliant cars are losing value.
Are they? Evidence please.
I was rather surprised at the market value of the non compliant diesel car that I got rid of in 2016 when it was already 6 years old. Seems to be holding its value rather well. Don't forget that the market value of a car is complicated and ULEZ compliance will be one of many, many factors and will only be of the slightest relevance to a small proportion of the potential buyers across the UK.
Buying a compliant car will inevitably cost you money.
Not really the right question - the question is whether, and to what extent, trading in a nominally non-compliant car for a compliant car will cost you more than it would have done without the ULEZ.
Buying cars is generally bad for the environment because making a new car has quite an impact.
Who said anything about trading in an old non-compliant car for a new compliant one? Certainly not me. Likely most people will be trading in an used non-compliant car for a used compliant one. So the environmental cost of manufacture is already baked in.
The government should be encouraging us to keep our cars for longer.
That is already happening, not through government edict, but because cars are more reliable and last longer than they used to. Apparently the average age of cars on the road now is greater than its ever been.
But this is classic 'nudge' policy - put in place something which encourages people to do something now that they would have done in any case in the near(ish) future.