''The revving while in neutral gets the main fan to spin fast enough to force air into the intake snorkel and keep the engine cool.'' Not quite true.
At fast idle or higher RPM, the fan does not force more air into the intake snorkel. It forces more air through the radiator, thus the better cooling. Whatever the size, make or model of air filter you install, none will drop your temperature by one single degree. Even removing the air filter completely will not bring any change.
An inter-cooler will not help solve your problem neither. It is not designed to correct a cooling system problem.
Your rad. cooling problem has nothing to do with air intake and will not be solved by spending whatever amount of money you wish on your intake system.
1) is your radiator clean, in perfect/unclogged condition?
2) All fans working as they should?
3) Is the expansion tank cap holding the prescribed pressure?
4) Is your water pump pumping as it should?
5) Is the serpentine belt tight, not slipping on the water pump pulley?
6) You have the right mix of anti-freeze/water?
7) Is you thermostat opening completely?
8) Any collapsed hoses?