Although my phenology idea didn't get too much attention, I quite liked it and know a simple way to do it if people are serious about this. Right now, the thread is a lot of talk but little hands-on stuff if you know what I mean
What you could do is make a matrix where you record different traits. The easiest way to do it is to keep traits binary, but you could have more values for each trait. What I mean is something like ..
0 is the ancestral state of the trait (usually means the trait is lacking) while 1 is the advanced or evolved form.
I just made a quick example and I see already it contains errors there, but disregard that

As you see, distorted guitar is the one trait they all have in common here, so that must have branched off quite early. In the similarity matrix, you can see King Crimson and Pig Destroyer (f.ex) have 2 traits in common -> the same value in two traits. King Crimson is more similar to Iron Maiden which it shares 3 traits with.
The above similarity matrix isn't very good but if you add more such variables to the mix, then perhaps you could make something of it. You could make a standard set of variables and have people add 1s and 0s for bands they like or think are important to your dataset.
You would have to identify the important traits of course but you've already discussed quite a few here I guess.
edit :
The similarity matrix can easily be represented visually through a variety of means, for example a phylogenetic tree (once you find an "ancestor" who should have primitive traits) which was my original suggestion.