Alternator ?

Nope.

Maybe if you have some massive stereo system, but in that case I don't think you're trying to build a performance car anyway.

I have 2 12"s in the trunk. But my RPMs rarely dip when driving & my headlights never dim though I'm running pulleys cuz I have a 1 farad cap in the trunk. That's another highly recommended mod if you're gonna run an upgraded system w/ underdrive pulleys. Either that or leave your stock alternator pulley w/ the underdriven water pump & smaller crank pulley.