If you have the room for it, run two wires. My buddy that's in the industry does this because of any place where dissimilar metals have to conduct, it can lead to oxidation and loss of current due to resistance.
Personally, I do agree, but I tend not to think that it's such a big deal. I would run two wires since keeps everything simpler overall. When you're troubleshooting and just having less connection points makes it easier, and in general reduces the chance failure. To most, it's probably less "clean" of an install running two wires, but in terms of electricity, it's a simpler.
If you run a distribution block, it's no big deal. In reality, you'll probably sell the car in less than a decade before any significant corrosion starts to occur. As long as your wire size is correct and your connection points are tight, you should be fine. Where I work, our units are designed to last 30+ years, so this is important to us.
Just as a quick explanation of what I'm talking about here is you're probably running bare copper wire into a nickle plated distribution block. Because they are two different metals conducting electricity, you run the risk of galvanic corrosion. The anodic index between the two differs by 0.05 (copper: -0.35 vs nickel: -0.30). This is actually pretty good. You want those numbers as close as possible. When they're close, there's less ion transfer between the anode and cathode (which will eventually lead to corrosion). It starts to matter more when you have more current, which is why no one really talks about it for something simple like decks and speakers.
Edit: the idea is, why add extra possible points of failure when you don't have to
Last edited by Vew; 12-21-2011 at 10:12 AM.
Reason: last thought