It's been said many times, the biggest cost to consider is the cost of depreciation. As a 65 plate, you'll lose far more to depreciation than you will to any increased fuel costs over the next three years, perhaps beyond.
If you've come from a Passat, you'll have far less headaches with Lexus reliability. Lower repair costs, less wasted time from breakdowns. Time is a cost.
As has been said, just enjoy the car! Only if you're doing frequent long distance motorway miles might you consider looking at something else.