I think it is more rational that the add/upload images should be in the manage gallery page, that is, on the edit gallery page, instead of having a page of it's own.
Currently, when uploading images, one has to go to 'Add gallery/images' page, upload the images, then choose a gallery for the images to be uploaded to. Now, when one has a great number of gallery, this will require scrolling down a long list of gallery names. Wouldn't it be more intuitive to just go to 'Manage Gallery' > 'Add New Gallery', then add/upload images from there? So it's just like creating posts.
Just a suggestion, though... I thought the 'Add gallery/images' page is just not necessary.