Jason,
I can't speak for your particular engine/transmission/read-end ratios etc., but it's generally accepted that a freer-flowing exhaust can help increase power and economy, but only if the stock exhaust is not built or designed properly for your needs. My stock exhaust had severe restrictions where it crossed over form the passengers side to the driver side, so an aftermarket system made a lot of difference for me. Most reputable exhaust system builders will publish charts which show gains over the stock system throughout the rpm range. Siimply increasing the diameter of the pipes/mufflers can have a negative effect 'cause header pipe length and diameter needs to be tuned for a particular rpm range, and a certain amount of back-pressure is required for proper operation. Check with Heddman, Doug Thorley, and others for your specific needs.
Intake 'turbo's', like the Helix and Tornado, are generally thought to have no appreciable performance advantage. This has been proven by independent testing organizations, so don't rely on 'user comments/reports' as they're usually all made up by the device manufacturer anyway. They typically create high and low pressure fuel/air layers (similar to those produced by a power boat propeller) , when what you really want is an even ratioed mixture of gas/air at the same pressure throughout the intake system and into the combustion chamber. A better use of your money would be for a good, low retriction air filter like the K&N, a performance chip tuner (caution - they can cause other problems) or, for best performance and economy, an add-on turbocharger. They're not cheap, but will give you the most bang for your buck - especially if you do a lot of mountain driving.
