I agree with Inertia- on older guys, the whole girly make-up thing just look WRONG! By the time a VK guy hits 25 he starts to lose the youthful cuteness that let him get away with the eyeliner and PVC he had before. Also, I can see how after so many years of doing make-up, guy would get tired of it. People who have only seen videos probably wouldn't notice just how much these guys sweat! The stage lighting is soooo hot, their costumes are hot and they're really nervous, so their make-up just drips offO_o;; I can see how after 5-10 years you'd get really sick of that^^;;
Younger bands can get away with just about anything in the costume department, but honestly their popularity depends not just on their costumes, but on how good their music, performance, crowd interaction, fan-handling and persona is. Also, naturally attractive guys will naturally have more fans, but they soon leave if they find out that he has a girlfriend, LOL. Japanese fans can afford to be fickle, but band-mans have to try very hard to get, keep and continue to get more fans... so of course at the start image is important, but it's still not the whole equation!
And personally I don't really care how Dir en Grey look as long as they keep making awesome original music \m/(-_-)\m/