Agree with previous poster about substantially editing and/or adding new material for the same reasons. You could also try publishing some of your poems in lit mags in the meantime -- I feel like if they are of publishable quality, without question you should include them (while noting when and where they were published.) It will come down to whether or not your work is a good fit for the school, not whether your work is a good fit for the world.
Same references should be fine. Unless they really loved your sample and the rest of your application, chances are, they didn't even read your reference letters (or read them hard enough) to remember them next year. Maybe that's pessimistic. But reference letters are all going to look pretty similar at the end of the day, right?
I applied to the same school a second time (haven't heard back) and I applied from fiction to poetry, so my writing sample looks a lot different.