Hey @CJtheTiger,
sorry for my radio silence here and thank you for updating the thread. In short: you drew all the right conclusions for the general case.
A MessageData solution can be quite performant when you know exactly what you are doing and when you must monitor either every object (in the sense of geometry) in the scene graph or at least many of them. For something like monitoring materials, shaders, or tags, the solution is mandatory anyways.
The tag solution on the other hand can become a bottle neck when the information flow becomes too expensive. Imagine such dependency propagation tag called DataTag, and you have 1000's of them in a scene. Each tag not only informs then one but multiple other nodes about changes of its host. Due to that there is also overlap, i.e., both DataTag DA and DataTag DB inform a target object T about changes of their host objects HA and HB. But for T this might be the "same" event and it then might be doing work twice. So, when stuff is getting complicated, you. are often better off with a MessageData solution, as you can consolidate things there.
Cheers,
Ferdinand
