Good idea to reuse them. I'm pretty sure I have petals too... Not sure a I'd make tutu with them, but it is definitely a super-cute discovery!
I agree with glue, if you are really, really careful, it would probably be fine. Good thing is, it would be easy to try a few different techniques on a small piece or two of tulle.
I'm pretty sure I've seen sewn tutus with things like petals in folded tulle, you might want to check them out.
-Jennifer- Full-time working mommy to Connor (August '09) and Maia (June '11)
Please forgive my typos, I'm often on an iPad which is difficult to edit (if I even noticed it changed a word