It will absolutely help you. In car audio there is a mod called, "The Big 3" which is basically getting bigger gauge wires from the battery ground to the chassis, from the block to the battery ground, and from the alternator power to the battery positive.
On a boat it's mainly getting the block grounded to the battery and the battery to the alternator since fiberglass doesn't really conduct electricity well.
You want to have as big and short of ground cables as you can here. Your system is only as powerful as your weakest link.
If you have 0 gauge wires going to your amps, that will mean nothing if your alternator can't keep up with the demand and pump as many amps into your batteries as is coming out. This is assuming of course that your batteries are being fed off the alternator and not just a bank meant for the stereo that gets charged up on land. This is also assuming that your alternator can keep up in the first place.
As for a fuse, it certainly couldn't hurt to put a fuse in line as added protection, but you don't necessarily need one from alternator to battery.
Wires I would upgrade if I were redoing the wiring:
-Ground from block to battery
-Power from alternator to battery
-Power from starter to battery
-All power and grounds in and out of perko switch
-All power and grounds from amps to battery
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