N/A tuneup for Euro 8G w/4G63 (I4/2.0L)

What type of modification would actually show some hp numbers?
(Denso Iridium installed).
A K&N RamPod is on its way from RPW, but I guess that would give approx 3-5hp (though Injen etc claims a 10%, or "up to 12hp gain) and a bit better throttle respons. Then I´m going for the RPW RD header-flexpipe and upgrade to 2 1/2" exhaust. Dunno where that will put me regarding hp.
From there , I don´t know. Cam and valvsprings? porting and polishing the head?
Where would the different upgrades put me approx from the original 137hp/100kw?

A local tuner strongly sugested to upgrade the cam as a first step, as airintake wouldn´t give me much of an upper. "Sportscam" would give me an additional 14-17hp. He´s a wellknown Rallycross champion in europe (Martin "Mr. Rallycross" Schance), but I can´t find anything online that supports this. Actually, from RPW, that what to do; air intake first, is the way to go. Cams even after exhaust.
Any views on this?