My impression is a lot of the Global Rackpsace videos seems to emphasize using it for effects, often for guitarists. I think that was the original emphasis of the developers.
There seems to be less material on using the Global Rackspaces for plugin instruments (within Kontakt, etc.)
I agree with the sentence in your first post. It is preferable to keep the Midi In Block in a local rackspace and put the plugin generating the audio in the Global Rackpsace. Then return it to the local rackspace for individualized effects, etc. for any processing. This give maximum flexibility, while getting the ram efficiency benefits of putting the plugin in the Global Rackspace.
The ability to simply route midi from a local rackspace to the Global Rackspace is not currently build into GP. [Edit: I believe in GP 5.xx, this function was added]. I am not sure if there are technical reasons or the Global Rackpspace was not originally conceived for this purpose (it was more viewed as a place to put effects?).
But, OSC works well for this purpose. It took me a bit of time (I am not too strong technically), but I think I am getting it (although I am still trying to perfect my understanding of this).
So, with this as I backdrop, in terms of plug-in instruments (via Kontakt or otherwise), I tend to think the Global Rackspace is a great place to put sample-heavy instruments that you use (without changing the samples, themselves) repeatedly. This is because I believe you save substantial ram as compared to duplicating those instruments in different local rackspaces.
The method of using the MIDI In block in the local rackspace and only using the sample-based plugin in the Global Rackspace gives you full flexibility for splits, layers and using these plugins the same rackspace with other instruments (in local rackspaces).
There are other techniques that are similar, like re-using the same rackspace by use of variations.
Also, within Kontakt, you can purge non-used samples. But, I think this would conflict with the idea of reusing the plugin in different variations or using it in the Global Rackspace. So, I think the purging technique is best used if you are just using that Kontakt “sound” in a single rackspace and not reusing it in multiple songs.
Okay, I’ve taken up enough space… Hah!
Jeff