The 2014 Audi A6 TDI. (Audi/ )

An automobile’s intrinsic worth depends on its overall usability — its applicable practicality — in a given driving environment. To the extent that a car is a bauble — a luxury toy not particularly useful for anything except speed and fair-weather handling — it is relatively impractical, thus not particularly valuable in the long run.

Intrinsic worth is diminished by a high purchase price and expensive ongoing maintenance. Just because you were excited or lustful enough to spend lots of money on a woefully impractical automobile does not mean someone else is inclined to make the same financial error in the resale market. Most people don’t want to finance someone else’s discarded fantasy.

That said, the 2014 Audi A6 TDI Quattro Prestige sedan, the subject of this week’s column, is a nearly perfect blend of luxury and common sense. It is a car with real value — worth every penny, in my humble estimation, of its $67,000 purchase price, including options costs and shipping charge.

The A6 TDI Quattro Prestige offers one of the most sumptuous interiors in the business. Yet it also comes loaded with common sense. It is equipped with an all-wheel-drive system that yields safe, confident motoring in weather fair or foul. It has a raft of comfort and advanced safety technologies offered at reasonable options prices. Dry-road handling is second to none in its class of luxury mid-size sedans. Wet-road performance beats most.

And there’s this: The diesel-fueled Audi A6 TDI Quattro Prestige delivers 24 miles per gallon in the city and 38 on the highway — an average of 29 miles per gallon. And it does so quietly and cleanly — thanks to sound-abatement and exhaust-treatment technologies worked out by Audi engineers and the company’s first-tier suppliers.

The downside: Gasoline-fueled A6 models start at $43,100. The A6 TDI Quattro Prestige starts at $$57,500, a difference of $14,400. That’s real money for most of us. And the cost of diesel fuel — $3.91 a gallon in the United States, compared with $3.68 for regular gasoline, seem disinviting.

The operative word here is “seem,” because it is a matter of perspective. Most gasoline-powered luxury cars require premium fuel, whose price is trending over $4 a gallon. In comparison, fueling a high-mileage diesel car could be a bargain.

I’m often taken to task by my peers in automotive journalism for emphasizing practicality, safety and intrinsic worth in my product reviews. Blame it on age. The older I get, the less interested I am in zoom-zoom wheel squealing and using an automotive badge to exemplify my self-worth. I’m finding truth in the notion that age nurtures wisdom. I now view my long-ago automotive concerns of youth as silly and completely unsustainable.

I’ve traveled worldwide witnessing some of the grandest displays of wealth and the very worst poverty. It is an imbalance that cannot peacefully last forever. People are amazing in that most of them want the same things, and some are willing to kill to get them in a world of limited resources.

But I run amiss. It is sufficient to say that I see stressors everywhere I go — especially in the matters of traffic congestion and pollution — and that the global automobile industry’s emphasis on zoom-zoom performance, usually on empty or abandoned roads, no longer makes sense to me.

That is why I so admire the 2014 Audi A6 Quattro TDI Prestige: It is more than a luxury automobile. It is a four-wheeled ode to common sense. It gets my vote here.

Nuts & Bolts
Audi A6 Quattro TDI

Bottom line: If you want an exceptionally well-made, high-performance, yet safe and efficient luxury sedan, you owe it to yourself to at least check out the Audi A6 Quattro TDI Prestige sedan.

Ride, acceleration, and handling: It gets top marks in all three. It can move from 0 to 60 mph in 5.5 seconds, fast enough to get you a speeding citation on most U.S. city streets.

Head-turning: It has an elegant, stately exterior with an interior worthy of the term “luxury” in both comfort and appearance.

Body style/layout: The 2014 Audi A6 Quattro TDI Prestige is a front engine, all-wheel-drive, four-door car with a traditional notchback trunk. Exterior body panels are aluminum. The chassis is made of high-strength, lightweight steel.

Engine/transmission: The car comes with a turbocharged (forced air), 24-valve 3.0-liter diesel-fueled engine (240 horsepower, 428 pound-feet of torque). The engine is linked to Audi’s eight-speed Tiptronic automatic transmission, which also can be operated manually via steering-wheel-mounted paddle shifters.

Capacities: Seating is for five people. Trunk cargo space with all seats in place is 14.1 cubic feet. The fuel tank holds 19.1 gallons of required ultra-low-sulfur (15 parts per million) diesel fuel, widely available in the United States.

Mileage: I got 34 miles per gallon in highway driving.

Safety: Standard equipment includes ventilated disc brakes on all four wheels, four-wheel anti-lock brake protection, emergency braking assistance, electronic brake-force distribution, electronic stability and traction control, and high-intensity-discharge headlamps.

Pricing: The 2014 Audi A6 Quattro TDI Prestige sedan starts at $57,500, with an estimated dealer’s invoice price of $48,300. Price as tested is $66,795, including $8,400 in options (Glacier White exterior paint, adaptive cruise control with stop/go engine technology, onboard navigation with Google mapping, top-view camera, Bose premium sound system and other items) and an $895 factory-to-dealer transportation charge. Estimated dealer’s price as tested is $56,108.