My first 5th gen was an early 2010 V6 2LT (vin 35xx). I drove that car for a couple of years before trading in on a 2011 2SS. That was a big leap in performance. I recently traded that car for a 13 2SS 1LE. While nowhere near that level of change, I wanted to chime in on the differences. I'm not a person to track cars, just a Camaro junkie who has regularly had them as daily drivers over the past ~30 years.
The suspension pieces work very well - the ride is very similar around town to a non-1LE, but you definitely notice the performance upgrade when cornering or driving spiritedly. My 2LT had springs and sways, and that was a rougher ride certainly. Not-so with the 1LE.
The 2011 2SS had a very bad case of the TR6060 rattles when releasing/pressing the clutch at low speeds in first gear - a problem that others have had. It was so bad in my car that folks were startled even 20 feet away at the grocery store or wherever. The new shifter/transmission and the gears are wonderful. No significant rattles, smooth shifts. The feel of the steering wheel and shifter is a noticeable upgrade.
This car is definitely quicker than my 2011. Both were LS3s. As others have said, this is probably due to the sum of the parts, not any one thing in particular other than the 3.91 gears. It pulls harder, feels stronger that my '11.
The rims and tires are very cool - they do have a downside (as all ZL1 and 1LE owners prolly know) - you will hear lots of rocks and road debris hitting your underside as they're sticky.
The 2012/2013 features also should be considered - power passenger seat, electric steering, revised dash, door lock button relocation, etc.
All in all I have no regrets, and believe that the 1LE addresses many of the things I would have wanted to improve on my 2011. These updates are under warranty though and I wouldn't have been able to achieve this level of performance for the $3500 asking price. It's an excellent value and you will feel a positive difference in driving experience.