The panel filter on the Omega is huge for a 200 BHP engine so it offers no noticeable restriction. The sensible way to tune an engine is to modify the parts that are the weakest link first. That means the exhaust manifolds, unfortunately. It's not always the easiest bits to bolt on that give you noticeable power gains, despite what the aftermarket tuning parts manufacturers will have you believe.
The induction system will have been designed not only for low noise but also to augment the breathing of the engine at low RPM. Put a shorter intake tract on it and you will lose low RPM torque and, if the original system has been designed well, you won't gain much if anything at higher RPM on an otherwise standard engine. It's not worth losing that low down torque unless you're going to get serious gains at higher RPM by fitting hotter cams, ported heads, etc, IMHO, especially on a heavy car like an Omega.
I have to say, modifying to increase noise alone seems a bit pointless. This comes from someone who is not averse to a bit of noise from time to time. My "other car" does tend to grunt a bit but largely for packaging reasons.

Mine's a London Pride, please, and a packet of cheese and onion crisps.
Kevin