I was scrolling through your stuff but this really popped out to me. The sort of monochromeness really makes this look awesome when you get pulled to the key looking thing she's holding xD. Amazing detail and really cool looking design. Nice work!
This would convey just as much awe, and would still definitely be feminine, without the cleavage. Is it really important that the Valkyrie is sexy? The warm palette already helps the good, welcoming image.
I agree that the cleavage isn't exactly necessary to the composition -for me-, but I think that's a decision for the artist to make. Also, just as "cleavage" and "feminine" are different words than "sexy" for a reason, one does not need to show cleavage to be sexy, which would be a possible continuance of your thoughts here.