Inziladun, I was interested in what you had to say here:
I think a big part of Denethor's issue was his lack of trust in anyone opposed to Sauron, if they weren't subordinate to him, or closely allied, as the Rohirrim. Really, it's amazing that he allowed Boromir to go to Rivendell at all. Makes one wonder if the thought of consulting Saruman about the dreams of Faramir and Boromir had crossed his mind, and, if so, why he didn't just do that.
The answer is very clear: Saruman was a rebel. When he was given the tenancy of Orthanc, still Gondorian territory, by Ruling Steward Beren, Denethor's ancestor and predecessor, it was on the understanding that he would accept his obligations as a tenant. Saruman later rebelled, effectively declaring his independence of Gondor. Why should Denethor, or any of his predecessors, trust Saruman, let alone let him into any of their confidences?
This is even
before Gandalf found out, due to his imprisonment, that Saruman was an enemy as well, in league with Sauron.