I recently watched about a dozen SCWs trying to tweak the AI and the likelihood of interventions, and the side with more armor always won (IIRC). Might have been a coincidence, though.Are you so sure about armour being important? Once Inf1918 is upgraded to Inf1936 things might change a bit.
Your point about reinforcements of gifted divisions is probably right, I haven't thought of that (and never tried to influence the war that way, it was just a quick idea). ESE and upgrades are definitely a huge factor for a human Spain, but how much do they matter to the AI? It less short on IC in general (with all the stuff it gets for free).