Yes, ditch those heavy steel wheels if you haven't already. Get some lighter wheels on there (perhaps some shorter tires), and it will make a world of difference.
I also ended up with a 2013 2LS, unfortunately they are the factory economizer and you are already at a disadvantage compared to the 1LS, 1/2LT cars because the 2LS has a 2.92 diff ratio to achieve that EPA rated 30 mpg hwy, while all of the other cars auto's got the 3.27 gears, and manuals got the 3.45, which is why I mention shorter tires because it will act like a lower (numerically higher) gear ratio without switching any expensive parts, it will however make your speedometer read slightly off depending on how short you go.
A good cold air intake, and some high flow cats will be worth the $$, but IMO lighter wheels, and shorter tires will be the best bang for your buck. After those, a ported throttle body is also worth while. After that if you still want to go faster, it's all in how much money you want to throw at it. Weight reduction is the best friend of a 2LS car. Shed as much weight as possible.