Underdrive pros and cons

I am concidering an underdrive pulley for my 4AFE toyota. I have found a decent 18% underdrive pulley. I know that I can gain a few ponies at the wheels, but I was wondering, what am I giving up? What potentially could be the downside of underdriving my other accessories...i.e. electrical/cooling inefficiencies etc?

FYI...93-95 corollas have a 3 piece crank pulley. The hub of the pulley which mounts to the crank, a rubber bushing that as far as I can tell acts as the dampener, and the grooved piece that the belts run on, which is pressed over the rubber ring and hub. After about 200k miles, the rubber shrinks a bit, and allows the outer grooved piece to slide laterally on the hub, which in turn, makes your engine a belt gobling mad man!!! Drilling 3 equally spaced holes into the pulley and inserting self tapping sheet metal screws will hold it in place, Im pretty sure this should only be used as a temporary fix though because there is nothing damping the vibrations (all this may be moot though as the inline 4 is internally balanced, and a local Toyota tech I know says the rubber ring is only there to keep the engine quiet). Anyway, this is why I want to replace the pulley in the first place, and Im not a fan of putting money into this car unless it makes the car faster.

Do a little more research into harmonic dampers - internal balance has nothing to do with it. On a high-power Miata, you'll toast the oil pump within 2000 miles if you pull the damper off. That's why there are better dampers available.

http://www.dinancars.com/bmw/technial-info/the-dangers-of-power-pulleys-and-understanding-the-harmonic-damper

http://www.atiperformanceproducts.com/products/dampers/101/index.htm

The rubber does a lot more than keep the engine quiet.

Some people have used underdrive pulleys on low-power (sub 200 rwhp) Miatas without failures for extended periods of time. But it's not worth it in my mind, spend your money on a new damper.

I DD my 5.0 SBF and don't like the slowing down of the alternator. That is my main concern. Over heating is not a problem in mine. So far I have burned one 3g alternator into oblivion. Due to my electric fan, extended idling causes a lack of voltage, even for my upgraded 3g alternator.

I couldn't tell you the percentage of underdrive or the power gained, but if I had it to do over again. I wouldn't have spent the money on pulleys...