I took a look at the stock intake manifold to see if I could identify any obvious restriction points. It seems like a fairly decent design although the intake runners don't seem to be "tuned" perfectly. I believe the optimal configuration for the manifolds (intake as well as exhaust) is an even-length design, where the distance from the throttle body to the intake valve(s) being equal/constant. Same thing for the headers, with the exhaust port opening to collector distance being equal (i.e. equal length primaries).
I'm not sure why an aftermarket aluminum (or plastic) manifold couldn't be designed which flows better or more consistently. I'm also not sure why the stocker being plastic precludes the swap for an aftermarket one (I thought someone said the manifold couldn't be changed b/c it was plastic).
One thought I have regarding this (currently hypothetical) quest for 300+ (crank) HP, is that all the components from air filter to muffler will probably need to be upgraded in order for this to be realized. In simple terms, a chain is only as strong as its weakest link. Any "flow restricting" point will obviate much of the advantages of the other mods. I'm pretty sure a good CAI, manifold, P+P, headers, high flow cats, dual exhaust and mufflers will cover things "soup to nuts". A performance cam and proper tune rounds it out and *should* give around 260rwhp. Maybe. Possibly. Hopefully...
I'm not sure why I'm a fan of N/A power over forced induction as I don't have enough data or evidence to suggest one is significantly better than the other. The N/A setup *seems* like it will weigh less, offer instant throttle response and possibly be more reliable.
I am wondering why manufacturers don't install blowers or turbos more often in cars. It seems like engineers spend countless hours developing technologies like OHC, 3-5 valve heads, variable valve timing, advanced computer control, lightweight internals, friction reducing materials, etc in their quest to squeeze an extra 10 - 25% more power out of a current engine, when they could just slap a supercharger on it and get 50% more real easy. There must be some advantage to N/A which I'm not aware of (or some problem with F/I). Any thoughts?