The fuel economy and maintenance cost "savings" of a Volvo over a Lexus is nearly non existent. The fuel economy of a 2011 IS350 and an S80 are identical yet the S80 has a worse resale value and higher repair costs. Maintenance costs can't be less on the S80 because repair costs are higher. Typically a vehicle with low maintenance costs also has low repair costs. Some maintenance costs are fixed so two different vehicles would have similar maintenance costs. As for a 2016 S80 vs an IS200T, the fuel economy "improvement" is only 3mpg while again, the maintenance costs should be similar while the depreciation and repair costs should be higher for the Volvo.
It probably depends on the model of Volvo, whereas lexus is reliably reliable. I know the previous s40's & such were based on mazdas, which shouldn't be too bad for major problems.