Might I ask what those aspects of femininity and masculinity we should be celebrating are?
Of course! 
I'm agnostic, bordering on atheist, but someone else (not sure exactly who, my apologies for the awful citation and the probably mangled quote, it's from memory) said, far more succinctly than I'm able: "The dance of the divine in both genders is not about lighting candles, chanting in a circle, gathering with the once-a-month goddess group or down at the local bar on arm-wrestling night trying to reclaim a lost ‘look at me, i create fire!’ masculine. it’s about being authentic, whole-in-what-we-project humans, embracing both the idle routine and the sacred within ourselves and within each other." Now, as I said, I'm happy that gods and goddesses fulfill a place in other people's lives, but I am skeptical myself. However, I like what this (unfortunately unremembered
) person had to say: each gender has something valuable and precious to contribute to existence, so why not celebrate both sides equally?
My personal opinion on what, exactly, we should celebrate?
Feminine: the cyclical beauty and pain of child bearing and reproduction, the innate connection to our offspring (a ton of interesting scientific data on this one as well, and an interesting debate point in and of itself when it come to the discussion about the biological imperative, if it exists, and if so, how much influence it has over our lives) and the language and communication skills gifted by the sex hormones that fire the "language nodes" in both hemispheres of our brains (of course- that one's of particular importance to me, both because of my background as a linguist and my current focus in studies and work)
Masculine: the enhanced capability to view situations through a logical filter and to better navigate spatial and logical situations due to the increased activity in their left hippocampi during such activities and the natural ability to appreciate their sexual partners and desire intimacy despite peccidillos like a few extra pounds around the hips or the godawful bangs that the hairstylist accidentally gave him/her (said sexual partner)- that's another interesting discussion which has its roots in neuroscience as well... but again, I digress.
None of that is to say that females can't develop the abilities of males and vice versa (well, except for the child birth thing), its just to say that in many examples of humanity, those specific traits are thought to be innate and directly related to the way our brains form as a result of our sex hormones. I think the differences are wonderful, and have lent to the perpetuation of the species, since they allow the masculine and the feminine to coexist in a more coherent manner.
On the other hand, I believe that the very thing that makes us sentient is our ability to rise above our "base programming" and act in a manner that might not ensure our survival as individuals or a species, but that might benefit others- so what the hell do I really know, anyway? 