I think the outfits and warpaint are a great way to create a "stage persona", but musically, they don't need it. It's not like I take them more (or less) serious because they dress a certain way. They've always got a nice humorous "tongue-in-cheek" sort of attitude, wouldn't want that to change for the world. It's just a form of expression that suits them, but it's not THE most important part of their identity, imho.
The new outfits still have to grow on me, obviously, but because I am 100% certain the new album will kick ass, I find the whole discussion displayed here a bit unnecessary. I don't agree with wm_crash about the importance of costumes. The music (+ lyrics) is their vessel to bring across any messages they have, not their costumes. So the parallels you draw are more or less an argument against your own case: the lyrics and music aren't just "lyrics and music", they are the essence. The costumes are just the first impression and visual addition that complete the "package". If they had great costumes but terrible music and/or lyrics, they wouldn't be as successful as they are now, or when it was the other way round (great music but no costumes)
It's a "gimmick" (god, I hate that word) that has helped them stand out and gain attention and if would be weird if they stopped wearing them, but it is (and always should) stay less important than the music. If the new album would suck (it doesn't, but IF) they could lose fans. If they decide to drop the outfits, they won't lose any fans. Only a couple of misguided poseurs perhaps (people who are only in it for the lulz, so to speak), but not the real fans who have supported them since Battle Metal came out (or some even before that). Real fans are in it for the music, and not because the band is wearing outfits.
If you listen to the CD, you're not constantly thinking "omg this band is cool, they dress up every night!", now are you? =P If you're into Cosplay and all that, you are bound to disagree with me. lol.
/end of respectful and friendly rant.