I has a really long explanation for this, but just accidentally deleted it. Ugh! (I really wish there was a preview window in the forum!)
So I'll give you the Cliff Notes version, the 1967 Shelby Mustang was the last of the original Carroll Shelby designs before Ford took more control of the operations. It was the most brutish looking of the Shelby Mustangs, as Shelby created a new fiberglass front end instead of just modifying the regular version. It was updated for the modern audience by painting it a stealthy color (gunmetal gray) instead of the usual flashy, bright muscle car colors. The Shelbys were known for their high HP to low weight ratio, which made them race-car quick and the modification made them some of the best handling muscle cars.
Only Nic Cage drove that "Eleanor" in the movie "Gone in Sixty Seconds (2000)".
http://imcdb.org/vehicle.php?id=2211
The movie was a remake of a car-guy cult-classic "Gone in 60 Seconds (1974)", which was a low-budget independent film from HB "Toby" Halicki. The original "Eleanor" was a 1971 Ford Mustang Sportsroof model.
http://imcdb.org/vehicle_4972-Ford-Mustang-1971.html
The producers probably picked the 1967 Shelby Mustang because it also resembled another car from a car-guy cult-classic film, "Bullitt", starring Steve McQueen and it's infamous chase scene with a 1968 Mustang fastback and Dodge Charger.
http://imcdb.org/vehicle_2159-Ford-Mustang-1968.html
I'm guessing the Keanu Reeves film you are thinking of is John Wick, Reeves drives a 1969 Mustang fastback, painted in a similar shade of gray. I'm guessing the producers of that film were inspired by "Eleanor", but that car is not her either.
http://imcdb.org/vehicle_739596-Ford-Mustang-1969.html
So the (updated) "Eleanor" is revered for representing one of the best performance cars of the muscle-car era combined with cool, menacing, testosterone-filled looks. (OF course it's Hollywood, so it's really all just an illusion)