I have been thinking about repetition and looping recently as a compositional tool. The best tracks that use looping, use reputation with variations. Think of the minimalists, for example Steve Reich and his piece Music for 18 Musicians. Listen to the start (its an hour long).
The piece I was listening to today was This place in Time by Colleen. What a gorgeous track for strings. Only just over 2 minutes long. The melody is basically four repeating notes - that's all. In fact it could be two notes which are then transposed down to give four. However, if you listen attentively, there are variations all the way through. These come from the harmony, the instrumentation, the texture and tempo (which slows) about half way through. Less is more with this piece. Lovely.
Finally, here is another great track featuring looping, Rockslide by Andrew Pekler. I hope you enjoy these.