CARMEL, N.Y. — For a speed-obsessed adolescent, it may be hard to believe that a shrink-wrapped sports car is not every driver’s object of desire.

But the type of car embodied by the BMW 6 Series — call it what you will, a Gran Turismo or a gentleman’s express — once commanded the highest levels of respect. Provocatively styled and emitting satisfied burps from a V-8, or even the occasional V-12, the classic two-plus-two luxury liner proclaimed its owner to be a lover of the good life and the fast lane.

But in recent years, particularly in the grungier recesses of the Internet, grand touring cars have become as easy a target as the private country club. The peach-fuzz ayatollahs of the auto Web, overflowing with opinions, see the luxury GTs — from BMW, Jaguar, Mercedes, Lexus or Cadillac — hovering beyond reach and dismiss them as decadent toys for the comfortably retired.

Their general wonderment is that anyone would waste money on a powerful car that’s not a Porsche 911, a Nissan GT-R or a cash-torching Italian exotic. They reason that the well-preserved buyers of cushier performance models have been addled by Centrum overdoses and CBS sitcoms. And to be honest, the 650i coupes and convertibles, redesigned for 2012, are not my idea of $100,000 perfectly spent either. But you don’t have to be a silver-haired fox, or a cougar, to grasp the Bimmer’s vault-on-wheels appeal.

Today’s 6 Series traces its philosophy to coupe models of the same designation sold in 1977-88, though it may not equal that car’s timeless styling. The revived 6 Series raced up the sales charts in 2004, despite a polarizing, coffin-back shape created by Chris Bangle, the company’s design director at the time.

In 2005, BMW sold nearly 10,000 of its 6 Series in the United States, but a harsh economy and buyers’ short attention spans cut sales to 2,400 last year.

The all-new 6 Series, which now shares the platform of the 7 Series and 5 Series sedans, is longer, lower and wider, including a nearly three-inch stretch in wheelbase and length. Adhering to GT tradition, the 6 Series remains blithely impractical, a stance that may evolve when BMW joins the 4-door coupe trend next year with the 6 Series Gran Coupe.

The convertible adds sex appeal with its motorized fabric top, a five-layer sandwich that is beautifully fitted and holds weather and noise at bay. The soft top also preserves trunk space, with a surprisingly useful 10.6 cubic feet of top-down room (12.3 cubic feet with the roof raised). A thoughtful carryover is the glass rear window, which operates separately from the flying-buttressed roof and powers up from the deck to serve as a wind deflector.

Coupe or convertible, the BMW’s cabin is blanketed in a new level of designer luxury, including my test 650i convertible’s ivory-and-black nappa leather interior. A 10.2-inch screen generously displays navigation, audio and vehicle data.

If you’ve guessed that the 6 Series can get freakishly expensive, congratulations. A new entry-level model, the 640i, holds the price to $74,475 for the coupe or $81,975 for the open-air version. The 640i gets an upgraded version of BMW’s 3-liter single-turbo in-line 6 with 315 horsepower and 330 pound-feet of torque. Aided by BMW’s eight-speed automatic transmission, that 640i coupe runs from zero to 60 mph in a healthy 5.5 seconds, quicker than last year’s V-8 model.

As with the 6-cylinder version of the flagship 7 Series sedan, the 640i also whips the V-8 version’s fuel economy with EPA ratings of 21 mpg in the city and 31 on the highway.

I tested the real brutes, the 650i versions of the coupe and convertible, priced at $83,875 for the coupe and $91,375 for the convertible. My test coupe and convertible each broke the six-figure barrier, at $100,825 and $105,025 respectively.

The new 6 Series adopts the size-down, power-up turbocharged strategy that’s sweeping the industry: BMW’s 4.4-liter twin-turbo V-8 spins up 400 horsepower and 450 pound-feet of torque. That’s 40 more horses and 90 more pound-feet than the 4.8-liter V-8 used previously. The result is a roiling ocean of power, available any time your right foot opens the floodgate. BMW says the V-8 coupe or convertible will surge to 60 mph in 4.9 seconds, a half-second quicker than before. The mileage rating is 15 mpg city and 23 highway.

An M6 version, coming in 2012, will have a twin-turbo V-8 producing roughly 560 horsepower. Yet I’m not sure why anyone would need the M, as the 6 already offers admirable power for a GT.

One might reasonably expect the hefty 6 (4,200 pounds for the coupe and 4,497 pounds for the ragtop) to feel doughy, but that’s not the case. It bends the laws of physics in the manner of other big Bimmers, applying electronic wizardry to tame challenging roads with unimaginable poise.

Toggling the switch of the standard Driving Dynamics system tweaks the reactions of the throttle, electric steering, adaptive shock absorbers and a stellar automatic transmission. Choose Active Roll Stabilization for $2,000 and a set of hydraulic actuators will tighten the antiroll bars for uncannily flat cornering, then loosen them for straight-line ride comfort. Another $1,750 brings Active Integral Steering, which quickens the steering ratio for low-speed maneuvers and adds rear-axle steering for improved stability.

With both of those optional onboard systems, along with chunky 20-inch wheels and tires, the 650i felt unflappable along Route 301 near Carmel.

Within the BMW, I was completely at peace, though it never reached the level of a mystical experience. As ever, the 6 Series seems at one with itself, not its driver — so relaxed and capable that its pilot seems to observe the action from a distance. All those digital ghosts result in a BMW that never transmits the lively sensations of a Porsche 911 or even a Mazda Miata.

Yet that’s the quality the whippersnappers refuse to acknowledge as desirable: Grand touring cars, whether Bentleys or BMWs, aren’t trying to be sports cars. Their laid-back drivers, secure in their station, wouldn’t have it any other way.

Told that a GT marks them as old and soft, owners might try their own condescending reply: Son, who cares about steering feel when you’ve only got one finger on the wheel?

Now, finish washing my car.

2012 BMW 6 Series

Base price: $74,475 (640i)

As tested: $100,825 (650i)

Type: Front-engine, front-wheel-drive luxury coupe (convertible option available)

Engine: 640i: 3-liter single turbo in-line V-6; 650i: 4.4-liter twin-turbo V-8; both sport an eight-speed automatic transmission

Mileage: 640i: 21 mpg city, 31 mpg highway; 650i: 15 mpg city, 23 mpg highway