IMO its only worth upgrading to a newer car if your going for something significantly different such as a MY07+, a different colour, a roadster or a Nismo kitted car. No point in buying another kuro, coupe My06 as the differences are not big enough.
When i changed from my 53 plate kuro I did so as I was about to spend £5k on a Nismo kit and Nismo rims plus tyres. That £5k would have been totally lost. Instead I used it to buy the 06 UY GT4 with Nismo kit, and then sold it and only lost about £500.