I would say another battery isnt needed for your current setup, I would simply do the big 3 if you havent and sound deaden ur car, I love the acoutical and daily driving difference after I sound deadenned my car (no roof, no floor)
Do the batt definitely. First of all, when the car is off, you're screwed. Also, 200 amps is the peak output of the alt, and even if it did that all the time, the amp pulls much more than 200 amps. You need a good battery(ies).
I say battery first. Deadening the doors wouldn't cost as much money or be as much of a hassle as running more 0/1gauge wiring and installing the battery.