Hi there. My 2 cents...your car's more than likely in tip top shape after its last visit to the repair shop but if you're itching for a change then go for it. Owning a diesel model myself I can tell you that it certainly demands more of my monthly income than my previous vehicle did (Nissan Murano) but the turbo diesel torque is quite unlike anything else I've experienced in a large SUV and I don't think I'll go back to petrol since it would require something like your 4.4 to deliver the same enjoyment and at current fuel prices (I live in South Africa) that's just not an option.
I suppose at the end of the day it's your money and why do we work if not to earn money to enjoy ourselves...