Raw vs 16 bit tiffs:
I do not have your nice camera; but converting to "raw-16 bits" blows up the size of the raw files considerably, usually by a factor 6. So my 10MB raws will be converted to 60MB tiffs. Adding one layer in Photoshop will double the size again - 120 MB. It is easy to see that Photoshop will blow up your 60MB raw with one added layer to over 700 MB, when exported as 16bit tiff.
I rarely use Photoshop with Aperture, only if it is unavoidable, because I need to do graphics composition - manipulation of the image that require the composition of two images into one. For all other adjustments I prefer to use the (hidden) layers provided by Aperture's brushes. This way I can profit from the lossless workflow in Aperture and do not need to blow up the file size.
If you look at the supported file types in the Aperture user manual, you see, that Aperture only promises to be able to store images with alpha channels (layers), but makes no promise to be able to display them correctly or to be able to adjust these images. Alpha channels are only required for compositing graphics, not for adjusting photos; and Aperture focusses on developing and adjusting photos, not general graphics.