Your opinion on a trade?

Hi guys,
MSV from Edmonton here. Would like to know your opinion/comments on a possible trade. Your input is very much appreciated!
I currently own a 2009 X5 3.0 xDrive Black on Saddle Brown/ Technology/Premium/Comfort with 68k KMs and am considering trading in for a BMW CPO 2009 X5 xDrive 35d Black on Beige/Technology/Premium/Comfort/Premium Sound with 73k KMs. (Priced at $50k CAD, yes I know ridiculously expensive but this is how it goes up here )
Advantages of the trade IMO: 1- Diesel engine 2- CPO Warranty 3- Will save on fuel 4- Premium Sound (not a huge deal for me)
Disadvantages: 1- Will get the first model year for the diesel engine 2- I like my saddle brown and am not a big fan of the beige interior 3- Will have to pay extra $$$ 4- I have heard higher maintenance cost for the diesel.
Questions for you: 1- Do you think this is a good trade? 2- How much extra $$$ should I pay for a fair deal? 3- is the fuel economy of the diesel engine really that much better?
Thanks in advance!