Just my final twopenneth on this, if there aren't some set parameters then the drafting process itself will be slightly pointless in my opinion. Dave will select essentially the line-up at Montreux 1982 with SRV headlining. Crosby Nick will have V Festival 1998 with Space headlining and I will have a complete mess of a festival, let's say Leeds 2002. No one will pick the same artists and we might just as well send our picks to Betty and be done with it.
And in that situation all that people will vote on, is which line-up contains their favourite bands and won't really be representative of a draft.
And thus to me, that's why silly categories are important. It then becomes quantifiable to a certain point. Let's say one of the categories is 10x platinum album singers. So I pick, let's say Dolly Parton and Dave Picks Aretha Franklin. At least then, we have a direct comparison both with advantages and disadvantages (no jokes about Dolly's knockers) but if you don't constrict it somewhat it's going to be an absolute nightmare.
How do you realistically compare Thelonius Monk with Outkast, Eminem with Buddy Holly, Rage Against the Machine with Loretta Lynn? The answer is you can't. So for me, we need a bit of direction in our picks so it isn't just a massive free for all.