Upload & Sell: Off
Yep I could certainly do that since the little Lacie drive allows me to keep each drive separate -- so I could have independently accessible SSD and ol' HD. Since the TB bus is so fast I should not seen any slowdown due to the shared connection.
However, (or should I say unfortunately), I think that even when using Aperture in Referenced mode -- i.e. and Aperture file with the actual originals living somewhere else (in your recommendation the slower HD) would only solve some of the problem since the Aperture file on the SSD would still contain all of the thumbnail, preview and some other files that rarely change and therefore maybe would best live on the HD as well.
I guess an alternative would be to used the Fusion drive with referenced files. I'm not sure if Fusion drive would separate files in one package (ie the managed Fusion library) between the two component drives of the Fusion volume. In my case the whole library is about 400GB -- which means the Aperture library package is actually larger than my SSD -- if Fusion keeps it all together then it would have to live in the slower HD portion, and I would see no benefit.
Not sure about this, but I thought I would test out the Fusion option first to see how it behaves. BTW one side-effect of the negative type that I discovered is that Snow Leopard cannot mount a Fusion drive so I would be limited to using it on a Mountain Lion or Lion Mac (don't have a machine to test with right now though).
Let me know what you think