In for the long haul

I'VE been driving a VW Passat turbodiesel wagon for a year now. I am concerned about the longevity of the engine, being a small engine working hard. I am thinking of trading it in on a Holden Sportwagon. I am thinking of the Berlina Sportwagon on gas, but am concerned about the economy compared to the VW, the power, the four-speed gearbox and running the gas engine in summer with the airconditioning full blast.