...gotta remember, a good ground is JUST as important as a good power source. as far as running multiple runs of wire for pos/neg, its kinda up to you what you want to do...if the batteries are paralleled close to each other, or connected w/ buss bars, it may be just a waste of money to do more than 1 set (300a alts and smaller). i guess there's no such thing as "overkill" in car audio though.
that score was just a quick burp w/ a sundown 3000d, extra batt. and fully loaded fi bl 12. box is 2.25@33hz, car peaked at 51hz. the extra power raised my tuning a bit, cause my normal amp (hifonics bx1606d) peaks at 49hz. this is my budget daily beater setup here in pullman. its in a 99 subaru impreza rs.
my other vehicle is soon to [hopefully] be a "groundpounder" w/ my 3000d and 2 18" nightshades haha