I don't think I often say to myself "this prayer would be impertinent to pray directly to Jesus; let me pray it to St. Joseph instead". While I would choose to pray to St. Joseph (for example) at times, the reason would depend on the kind of prayer. One scenario that would come closest is perhaps when a petition is trivial. "St. Joseph, patron od carpenters, help me reach this bolt". Here, it would seem presumptious to ask Christ to help me handling the spanner.
More substantial is contemplative prayer such as the Rosary. There the entire Gospel event is contemplated, for example, the flight to Egypt. Joseph might be the central figure of the contemplated event as I concentrate on his task protecting his family from an evil tyrant with the humble resources at his disposal. The prayer might ask St. Joseph to teach me similar qualities. It would be a mental convolution to ask Christ to impart to me the qualities of St. Joseph; it seems more straightforward to simply ask St. Joseph himself.
Another aspect that is useful for our Protestant friends to grasp is that the prayer is often non-verbal. If I were to attempt to verbalize the exact qualities of St. Joseph, the purpose of the contemplation would be 90% defeated; rather than contemplating I would be authoring. Hence the verbalized part is a memorized formula often only loosely connected to the object of contemplation. "Hail Mary full of grace..." is what the lips say, but the mind is, in my example, focused on Joseph, and the mind is free from the task of verbalizing. The beads in my hand also help maintaining the focus: they movement of the beads mark the special time spent with the object of the prayer -- which often is Christ directly, but always Christ at least indirectly.
Does th Rosary prayer, or prayer to St. Joseph take away the time I spend directly with Jesus in the similar contemplation? It is like saying that spending time with my children takes away from my relationship with my wife who bore these children, and who rejoices in the knowledge that I am a good father to them and spend time with them. The reality is that my love for her grows in this activity even though the children are in focus, and my wife might be taking a well deserved rest in another room. I go to Mass weekly, often twice a week. I read the gospel daily. The Eucharist is the highest form of prayer and it is prayer to Jesus, uninterrupted and intimate. It might shock you guys, but I eat His flesh each time I go. Prayers to saints make my prayer life richer and they draw me closer to Him.
I'm sorry but this "humility" in prayer thing has completely lost me. I can think of no greater "humility" than understanding that we have fallen from God's grace, God have had to restore us, and that we are solely dependent upon His provincial hand to substain us. Going before Mary, Joseph, or "Saint" Sir Thomas More, seems silly when one can go directly to the throne of God.
I'm told by many here (Catholics included) (and wrongly I might add) that Jesus stands at "the door and knocks" and all we need to open that door. Well, if that's the case, why then don't you take ALL your prayers to Him since He wants to have fellowship with you?
There is NOTHING St. Joseph is going to teach you. There is only ONE teacher and it's not any of the "saints".
And if you don't think kids take away time from your wife, then, as an experiment, send them off to camp. You'll find out how wrong this analogy is.