Well, clearly, such tournament exist in order to encourage female participation and interest in chess, overall.
It's not a question of "whether the world :needs: it or not (in general)", since women want it to be held, it is quite ok and I don't see a problem with it. If I were a woman though (now there's a thought experiment), I would still decline participating in such an event, as it would imply that I was unable to compete on par with men just because of my gender.
As someone already mentioned, similar world championships could be held, in principle, for any minority group (not necessarily a minority group in general, but a minority group in chess circles)... though I think they wouldn't be given as much credit as the female world championship gets. I mean, how do you assume the public would respond to a "gay chess world champion" (or black or ... ) or something if such a thing existed as a formal title? Do you think such events would have been covered by press or top chess websites? Do you think people (other than the minorities in question) would cheer for them and encourage them to play in these separate events?
I think that part of the reason that the male players :are: interested in the outcome of female tournaments is, well... because we like seeing beutiful smart women playing chess, as simple as that ;) ... so the whole thing has more layers than what meets the eye (I think)
I don't think that the Women's World Champion, Hou Yifan, has anything about her that makes her deserve more attention than a male equally rated to her. Unless you want to look at rarity as a concrete attribute, which I really don't, at all! If she was born a man, she wouldn't get nearly as much attention, so she can consider herself lucky that not only was she able to become really good, she won the coin toss too, and that's the vital part. If you lose that, you have to work harder for equal attention. It's so unfortunate that society is that way -- that when a beautiful woman achieves something it's suddenly better. So superficial.
You don't promote something by giving a group an unfair advantage; you promote it by giving this group words of encouragement! I have never understood why we have to have a bias towards something (giving women something easier) in order for it to count as encouragement. I think you can, and should, encourage someone, while remaining unbiased!