It's not just the theromostat itself that provides the horsepower. When used in conjunction with the Jet chip it increases the HP.
Some guys change the thermostat to the 180, just to start the cooling sooner, and from the perspective of cooling it does help. For awhile I ran a 160, but in the winter it was just to low to properly heat, so I went back to the 180. In warmer climates, the 160 works well.
Essentially what the Jet chip is doing is changing the computers timeing curve. The temperature tells the computer as to when the engine is at temp and with the O2 sensors provide a properly air/fuel ratio. At the same time, the Jet chip advances the spark. So with a hotter spark, slightly more fuel to air ratio, the result is then more HP.
Part of the requirement is to be able to injest more air and be able to expel the same. This is one reason that Jet has 2 chips, one for unmodified and one for modified. The unmodified uses stock air and exhaust and provides a marginal HP and MPG gain. The modified provides large HP gain and maybe a MPG gain.
Hypertech uses a reprograming device to reprogram your computer to take advantage of modified intake/exhaust vehicle. It will allow the use of regular or high octane fuel and you can mix and match what you want for the best performance.
Is it worth the money. If you do solely wheelin, probably not. Generally, your not in the higher RPM range long enough to take advantage of the HP/Torque gain. If you do a fair amount of towing or travel mountains at high speed, it's probably worth it.
If you are looking at it for MPG gain, it is definately NOT worth the investment because you may or may not even get a MPG gain. Depends on driving habits, age of engine, and mods to engine.
Can you feel the HP gain. If you are physically tuned to the performance of our vehicle, yes. You will feel the difference. Can you beat your buddy in the Viper off the line with it, don't count on it.