If we keep on asking and asking a human to keep on giving us things, that human will eventfully lose his or he patience. There is a limit and then the giver will feel be used.
However, this is not true when you ask things or favors from God.
God with his infinite goodness and might will never get tired of answering you. He would appreciate that you thank him for what you get. Instead of asking him" God bless America" why not ask "God bless everyone in this universe". For God this added blessing is no big deal.