B20VtecVillain

Don't know if anyone here has experience with the platform but I figure what the hell, I'll give it a shot.
My entry AutoX/track car is a 2005 Mazda SP23. The thing handles great, is very predictable and easy to throw around in twisties, but it is lacking power GREATLY. So far I have all the basic bolt ons; Injen Cold air, Vibrant race header, TruBenz 2.5" exhaust with Magnaflow high flow cat and muffler. (Header deletes first pre-cat), Cossworth Intake manifold, ported stock TB (approx 63mm) and Custom ecu flash using MazdaEdit software (Dynotronics). On 93 pump it made 156whp/151wtq. This is definately an Improvment over my baseline (131/128 with just Injen intake) but it still doesn't have the power I would like. Without going into a FI setup, is there any way to squeeze more power out of this thing. Anyone have experience with aftermarket cams and the 2.0/2.3 MZR/Duratec engine platform? I have been suggested to just do a 2.5 engine swap from a Ford Fusion or newer Mazda 3, as it looks like they are laying down in the 170s with bolt ons and tuning, but I really don't want to do a $2500 engine swap for 15 hp/TQ. Right now the power curve is very linear, great for the track I just wish there was more power. On the straights I get owned. (Under 160whp and 2950# car + 215# driver= slow) The top end is also, in my opinion, very weak compared to other 4 bangers , some even using less displacement.
The aftermarket intake manifold definately helped the top end, though not until after tuning did it make any power. Actually, on the stock ecu map the manifold actually made about 8-10 hp/TQ LESS at peak than the stock piece, but after tuning and bringing the Rev limit up it has shown marked improvement. I definately would like to try building the head and using more aggressive cams, but I have not found much at all as far as what components people have used and what the outcomes were, so I decided to try and reach out on HT. any/all input is appreciated!