Well I can give you a bit of insight into your question, but I have to ask you a question. Are the set of cams you're looking into more for sound or for performance? I know when I got my Hot Rods installed, I only gained like 4-5 lbft of torque and like 8 rwhp, but the sound was killer. There are other cams out there which will provide more power. The full exhaust, long tubes + O/R h-pipe netted me about 25 rwhp when I did it. So like another poster said, you're looking at mid 30s overall gain. The h-pipe should get you another 10 or so depending on tune, etc.
As for the nitrous as some people stated, it is a nice inexpensive temporary power increase, but if you use it enough and are careless doing so, it can become very expensive. Best overall bang for the buck is the CAI + tune, which you said you've already done. Next would be the exhaust.
Also, FI is not a bad way to go but I like the idea of staying all motor. Plus we all know, bolt-ons help bolt-ons.
Hope I could help some.