We agree more than one might think. First, I agree that the prosperity that comes from tithing is an outpouring from heaven, including a recognition of what is true wealth. The fine cars are what I believe James is talking about when he warns woe to those who are rich. "Let the poor say 'I am rich.'" So, I watched for an honest expression of prosperity, peace, joy, giving generously, and a freedom from the poisonous riches declared by the world.
Second, in my role as a watchman, I have found both greater faithfulness and effectiveness as I was faithful, first in tithing, then in giving. The world has experienced less of the "devourer" since then. As I have watched others get restless about sin in the world, and asked God about it, He has told me that deep inside many sense their own guilt, through their robbing God in not tithing or giving. So, my prophetic experience confirms this reasonable argument.
Third, the law is a tutor to lead to Christ, and our righteousness must exceed that of the Scribes and Pharisees for us to truly receive salvation. Jesus commended them for at least tithing. A "by this you know" which we look at to "be sure of our calling and election," is our giving. Believers ought not tithe, but they ought to be giving way above the tithe. If they are not, they ought to question their salvation, and start using the tithe as the minimum standard of their giving. Many "believe" they are saved, but are deluded, according to the parables about salvation given by Jesus. "Tithing," as an act of "buying the truth" and as a refresher course with the tutor, will squelch this delusion.