If you can get 20Kwatw with modifying a stock air-box, AND while maintaining filtration quality, then I'd hazard that someone at Mazda has taken their eye off the ball. I doubt that very much.
Further I don't consider $200, or often less, a great expense for the option I proposed, noting that I stay well clear of CAI's as I consider they offer a few disdvantages with very few advantages over a good SRI, and either will outdo any air-box mod anytime - yet will still never, ever get you 20Kwatw.
You may indeed be right, but I remain to be convinced.
CP_e Standback & PNP; CP_e 3" SS Downpipe; Corksport FMIC with Top-mount K&N filter & OEM Ram CAI; Turbosmart BOV; Dashhawk; Prosport Boost Guage; JBR solid shift bushes; DBA 4000 Wiper-Slot front rotors; Hawk Ferro-Carbon HPS Street front brake pads (@ 69,000km); Sumitomo HTRZIII's in 225/45 x 18