Are you referring to repetition of the output, or of the input? I think the difference is fundamental but possibly not important in the end. Based on the Comprehensible Input Hypthesis, output, or repeating the message over and over in speech after hearing it, wouldn't aid acquisition at all. It would be more akin to memorization. If you're referring to listening to the message repeatedly, that would be more likely to help, but I don't think it would be ideal input. Effective input must be comprehensible, but if the message is comprehensible, you don't really gain input by listening to it repeatedly in the same way, and, furthermore, by listening to it repeatedly, the message itself is no longer interesting or compelling. I also suspect that repetition of a given structure or vocabulary word is more effective when it's repeated in a variety of messages and contexts.