It always suprises me how people want to undo the work of the development engineers.
If you are going racing then you want to change the engine charcteristics, and probably the engine maps too and I can see the point.
On a road car the ECU is mapped to behave its miserable self with the original equipment in place, and as you largely cant fiddle with the map its almost certain that you will have worse emissions for messing with it, and almost definitely more noise, The air flow is messed with to produce the best compromise for road use and for certifications. The equipment is designed to ensure the air is filtered and available at the right place, pressure and time. It is also tuned for sound and to avoid resonance. ECU's read athmospheric pressure so it must be important to keep within the preset limits for best operation.
I understand the desire to tweak and fiddle but persoanally I think the current day resitrictionson whats going to improve things are removal of rough edges and burrs on the pipes and more importantly immaculate service records. The cost of even a secon hand air box are eye watering these days and I would be frightened of wrecking one.
It would be fun to see rolling road outputs on some of the minor mods which are done so often and see which have effects, both bad and good.
One of the reasons I loved the Panda 100 so much was that it ws beautifully quiet and refined and when driven off sounded reaaly smooth, while being able to scare the socks of all manner of bigger cars if pushed hard. Noise just attracts the wrong kind of attention!