There is a fundamental underlying question here: should men and women in pinball be considered equal in terms of potential or not?
Some sports fundamentally divide by sex (such as tennis) because of the height and strength advantage of men (and mix it up in other ways, such as in the mixed doubles comp). Others (someone pointed out equestrian events) do not.
If we assume that women in pinball are just as capable as men, running a separate women's event seems out of place in the sense that we might as well have a separate event for any other sub-group that is assumed to be equally capable, such as Asians, 35-45 year olds (the "Midlife Crisis Invitational"…), past runner-ups in a major (hi Josh!), or—God forbid—African Americans. In other words, why single out women rather than any other arbitrary sub-group, if women are just as capable as men?
If we assume that women in pinball are not as capable as men, running a separate women's event seems totally appropriate, just as we don't think twice about having a children's event or trophy, a beginner's event, a B division at Pinburgh, and so on.
If we do assume that women are just as capable as men in pinball, and that the under-representation of women is a numbers game, then a separate women's event runs the risk of being seen by some as a second-grade competition, with a concomitant ring of discrimination and condescension.
Seeing that women's events are for women, I'd let the women decide. If there is enough interest, why not? Try it out and see how a big a response you get. If some women want to measure themselves against everyone rather than women only, they can choose not to participate in the women's events, so no-one would be the worse off for it.
In terms of encouraging participation, women-only events sound like a good idea to me. Due to the discrimination and sexism that has been mentioned here in the past, I suspect that some women feel more comfortable in a women-only environment. (Why else would women have started women-only leagues?)
Women's events might help to bring more women into the sport, which would be really nice to see. And, heck, it's more pinball. That can't be bad, can it?