Good idea.When it comes to the finals, you can create groups which are based on the votes of previous rounds instead of grouping them randomly. That'd be fair, don't you think ?
Btw. Death Magnetic is my favorite Metallica album, but I don't think songs from that album stand any chance against 80's songs. As a matter of fact, only songs from the 80's ended up in Metallica Survivor's Top 10.