So, I figured out the issue that prompted all of this and it took damn near forever. Apparently feature level 9.x devices can't copy GPU data to resources (e.g. textures) that have a shader binding flag set to CPU accessible resources. And apparently the D3DX functions to save the texture does exactly that. It copies the GPU texture to a CPU staging texture and writes that out (makes sense, reading from the video device is a no-no). Unfortunately my device object just says "fark it" and promptly dies when this happens, which seems like a driver problem. Anyway, it's fixed now. Not that it matters, but it was painful and could have meant the end to Direct3D 9 video card support in Gorgon (which no one probably really cares about anyway).
Unfortunately the fix comes at a price. Part of that price is increased memory usage. It's painful enough to have to create temporary textures when converting to a format that's not able to accept anything by standard RGBA 32 bit formatting, but with the feature level 9.x there needs to be another temporary texture that doesn't have a shader binding flag. It's kind of gross. The other part is that the only way to get it without a shader binding is to create the texture as a render target (unordered access views would have been nice, but they're for Direct3D 11 devices only), so that limits the number of formats that can be used when saving.
Anyway, thought I'd throw that out there.