This all depends on what type of intake you choose. I have had both short ram and cold air, there's a huge difference between the two.
The cold air reduces your low end torque but increases your high end.
The short ram increases your low end torque but decreases your high end.
This is not as dramatic if you install a MAFS from
http://www.jetchip.com
Which ever you install, you WILL notice better throttle response.
Also, aftermarket exhaust helps a lot too. Once your getting higher volume of air to the engine, you need to be able to exhaust it. TRD, Borla, etc.
Overall, with all of this installed, you might gain 5-8 horsepower. And you will probably see improvements in your gas mileage.
So for just under $1000.00, you too can be frustrated with the results! Lol!