Truth is, I just hadn't thought to use the command to remove unused nodes in the Render Tree because I'm usually pretty organized and delete nodes on my own as soon as I've made a change.
But after messing around with this feature for a good while now I've decided it's actually a *good* thing that duplicate texture nodes are sent along. Because when you update, the new nodes are attached where necessary, depending on type, and the older nodes are detached, but the textures remain attached to an image node. So it's all still set up if you want to change again.
And the "mess" is nothing that ctrl+R can't fix quickly. :D
And here I was complaining that Mud/Softimage does this, while Mud/Maya doesn't, but with Mud/Maya you lose the ability to re-attach older nodes and would have to set them up manually again.
So if any of you Softimage developers read this, please don't "fix" this feature - Bug or not, intentional or not, it's incredibly useful. :)
Who needs GoZ... to hell with waiting for that - the Mudbox/Softimage combo works extremely well with texture maps, normals, displacements, spec, illumination, AO... and of course GoZ can't send an organized group of individual blendshapes. Well, even if it could, it can't send *anything* to Softimage. ;)