I finally got the time to do some temperature and vacuum measurements on the stock intake system.
I used OBDII readings via my Innovate OT-2  to iPhone.
The mesurements was done with 24 C ambient.

First snapshot was after warming up the car and idling for about 10 minutes besides the road:

I then did a quick WOT run on a 500 m straight road accelerating into 4th gear (1.8l 5-speed).
The 2 min time diff is me packing up and waiting for clear traffic.

The result is a massive 21 C reduction in IAT  and 19 C for the coolant temp.
I then continued in normal traffic to another stretch of road that goes up a hill.
This is the result after flooring running trough the gears up to 160 kph:

Thats 2 C above ambient and coolant temp down to 79 C.

But what about pressure drop after the stock intake, filter, MAF, flex pipe  ?
I connected my AHJ digital manometer to the vacuum soruce for the purge valve as the FSM suggested.

Readings was done both with the OT-2 via OBD2 (MAP)  and the manometer.
The readings on the manometer was fluctuating a lot but the min vacuum I could read was the same as the OBDII value:   0.05 psi pressure drop at 7K rpm in 3rd gear under load.
That is 1.4 inches of water which is supposed to be extremely good for a stock intake according to autospeed.com :  http://www.autospeed.com/cms/article.html?&A=112734

But what if the car was modified with headers, exhaust, ECU tune ?
Actually my car has those mods including a 7200 red line.

Based on my measurements I would say a cold air intake would do nothing for my car.
The final test will be to log temperatures on the track.  That might happen on the 28.