Fair enough dude... in this case, it might not be the earthing.
Although my VK was quite happy to run 3 amps, 4 speakers, and a sub, with two 12" thermo fans on the stocker. The high-beams dimmed very slightly with a lot of bass, but other than that, no problems.
I actually suggested changing the original earth AND positive battery cables over, and cleaning the surface for a good contact. As for my R33... the power cabling is about 2 feet also. It goes directly into a fuse/relay box, and the earth straps to the body next to the battery. So even this upgrade for me made a huge difference... I figure that i'm drawing power from my battery, not my alternator... the alternator should charge the battery, and if it's really too weak and you run everything on full ball all the time, then eventually the battery will discharge completely as the alternator cannot keep up with it.
Then again, i've always had really good batteries in my cars. It'd be interesting to see how your new alternator goes! I wonder what will fit? Maybe a VQ item or something?