I've been to these slam festivals and it's a strange feeling to see how competition brings out pain in people, especially in poetry where there are a lot of vulnerable people putting out their work. Sometimes you get very performance-oriented people who aren't as solid as writers, too. However, on the flip side of the debate, spoken word and slams are also a window of opportunity for those uninterested in poetry to become exposed to and drawn into the poetry scene. It gets people involved in poetry when they normally wouldn't be. Frankly, poetry readings can, at times, be very boring.
Music creates an aura.
The poetry is not as intense without it. Whether or not one means of expression is any better or worse than the other doesn't appear to matter in the end, so long as poetry is brought to life. Masses read books and masses see performances, so I don't see anything wrong with giving the best of both worlds. When you're giving from the soul, I don't think the medium or genre should matter.