An interesting thread, and one that crops up on all of the previous model specific forums that I frequent. Only the very expensive intakes will yield any power gains - such as a well designed k&n unit - but gains will be minimal and will usually only appear higher in the rev range, often to the detriment of low range power. As echoed above on an Omega I do not think you will be getting that much cool air from under the bonnet anyway. You have to ask yourself £180 for 5bhp - is it worth it - a good service will yield more than that?
I used to always chuck a k&n panel filter in my rigs but after seeing how poorly they filtrate compared to paper and how quickly all of that oil gets on the maf and throttle body - I won’t be doing it with my Omega.
I have to confess I don’t like the idea of putting an intake on the lower grille - surely that’s just asking for trouble? Last time I checked I don’t think engines run too well on water, slurp!
-Dave