The problem is in the vainness, not in repetition. In how many different ways can we bless our food? How many original prayers-original in the sense of novel or unusual language-can we offer?
God is not offended by repetition, so long as the words are spoken from the heart and are sincere. The heavens withdraw themselves, however, in the face of vanity. Something is vain when it is empty, meaningless, or hollow.
Whenever our prayers are meaningless and thus become trite or ritualistic religious jargon, having no feeling or emanating from a duplicitous heart, they accomplish little.