I've heard that you have to buy a heat shield for it to even be noticeable.

CA l is the one that goes outside of the engine bay. Do you mean a RAM (Ram Ait Intake)? They work better with a heat shield.

Pushing more air into the motor does not help much unless you increase the air comming out and the fuel added.

Do not get an aftermarket intake on a wrx. Yes u will gain some power since u will lean out ur air/fuel mixture however if u plan on modifying further u will find that aftermarket EM will not provide OTS maps for it. Intakes r good when u r making 300+whp, the stock turbo will push all the air it needs out of the stock setup it does not move much in terms of cfm is 428 l believe is the number for the TD04. Do not know what some of my abbrev is r for?. You need to do some research first.

yea it will but the gains arent worth the money on a forced induction vehicle.. you would be better taking ur car to a shop and having your factory airbox modified.. go check it our and ask some questions

The stock intake flows enough air for up to 300 hp.

Intakes r generally more of a problem than a benefit on WRXs due to throwing off A/F ratios. There is better ways to spend ur $200 or whatever it costs, but if u MUST have an aftermarket intake, then look at SPT or Cobb is short ram intakes.

If u want more hp, then look at EM, such as Cobb is Accessport, TurboXS is Utec, Ecutek, etc. For instance, Cobb is AP is worth 25 hp on a stock WRX, & combined with an uppipe & downpipe, it is worth 50 hp over stock. This is the easiest path for upgrade & has proven to be reliable. You can look at Cobb is site for the components needed for each 'stage' & the expected hp increase.

Hope this helps.