You make a lot of good points, Dodger, and I agree that Dean is a perfectionist who is used to having to shoulder impossible burdens, expects far too much of himself and of others, tries to have estel in all the wrong things, and needs to rethink a lot of ingrained behaviors and thought patterns. And I'll grant that God's not a vending machine or a magic fix-it device. But I still think the sticking point has been and will continue to be DSOTM--the one time Dean sought God out, God essentially slammed the door in his face. I may be reading too much of myself into Dean here, but I think he could have accepted "You already have what you need, and you'll know what to do when the time comes." He wouldn't have liked that answer, but he could have lived with it because it wouldn't have implied abandonment. But that wasn't what Joshua said, and Dean didn't have the relationship with God that he had with John to be able to hear "Back off, it's not my problem" and understand "I trust you to do this yourself because you're a grown man and fully capable of using the gifts I gave you"--assuming that's what the statement meant. I'm not entirely sure that it did.
So the question remains whether God in that universe is worthy of the trust Dean wants to place in something other than himself. What Dean inferred in DSOTM is that God doesn't care--"Just another deadbeat dad with a bunch of excuses" who expects him to do the impossible when he's running on empty and never gives him a day off. And he's likely to need tangible evidence to the contrary before he can allow himself to trust God at all.
(And I'm likely to keep dreaming of dragging the boys into this universe, where God does answer the phone on the first ring!)