id think port and polish would make better gains than headers, but w/o headers theyd be pretty much useless...good CAI, p&p, cam, headers, and a reflash. nitrous is nice, but i dont want to have to keep refilling a tank for my power.
Nitrous is probably the cheepest way to gain 50-100hp. For around $500 for a kit you can have that. Nitrous says that you can add up to 50% of what the factory HP output is. So on a new 190hp 4.3, 95hp is 1/2. Since the motor is almost bulletproof I have seen stock motors running 150hp. If done right, it wont hurt your motor.
The wet system is a more reliable kit simply due to the fact that you can actually set it up a little more fuel rich with the jetting. with the dry kit, you cant do that. So if for some reason it goes too lean, or if the regulator isnt working properly...........BANG!!
Well in all my 16 years of messing with cars, I have only used Nitrous systems. I dont know how other people/companies have their product. As long as the unit has a nitrous and a fuel line going into the fogger, you are good.