Yeah it does get cheaper, by waiting, but only a little bit.
First you dont have to pay the circulation tax for 6months (cost is between 100 - 1767 euro/year+ depending on age and CO2 emissions), and the UK tax disk is always less than that. Then if you're lucky the value of the car goes down because its 6months older (depreciation) and higher mileage so the registration value and therefore tax is a little lower. I think I saved a little on the valuation, it definitely went down by waiting 6months, its not just year cut-off but pro-rated somehow I think.
I think there are boundary cases were it makes a bigger difference also, eg if the car is under 6months old and you can wait until it is over 6months old you dont have to pay VAT on its registration value (another 18%).
(Also you can save 6months interest or bank loan to pay it
And who knows maybe you coincidentally have a change in circumstances and have to go back to your previous country residence, then you never have to pay it. There are no refunds once you've paid it, never be in a hurry to pay something that can be paid later!
Also something I didnt understand at first, but when you see local advertised car prices you think wow its cheap to import, but the trick is if you tried to resell an imported car, you wouldnt get that price.
People put a premium on local cars because of lower mileage and lower rust (no exposure to ice, road salt etc). So there are two prices: local car or imported car, you have to compare like with like (if you're factoring inf eg trading in or reselling your imported car after some time).
But some anomaly here I just tried the adt registration tax site
and it says I'd have to pay eur1400 instead of the eur1200 I paid 2 years ago. Thats got to be wrong its now two years older, its registration value is eur1750 vs eur 2400 2 years ago (looks ok) but the reg tax is very wrong and its mileage is 10k higher. Calculating the current registration tax myself manually from info in this:
I think correct would be eur540.
Or maybe they significantly changed the tax formula since that pdf was published? Weird.