I think it depends on your setup, but CAIs are not always beneficial in vehicles, especially on some of the newer models.
1) The heat that a CAI can inject that a stock box system may not can make notable differences, especially on boosted autos. Not all do, but there are only so many places to route CAI on vehicles, so you may not have many choices.
2) Some newer models actually have as much or, in some cases, more airflow as/than needed. This may be hard for the average person to calculated, but opening your intake up too much can be a bad thing. Some boosted cars have no need to open the intake up prior to opening up the exhaust more. Bottlenecks in a system can completely negate performance improvement (and even harm it where a tuned ECM, etc., is involved.