I've heard about them, but have never been to one in person. I've heard them called a living funeral by some people and a celebration of life by others. They sound like a great idea to me! Even though it's not meant to be somber, I'm sure some folks would find it difficult to attend. If your aunt is up to though, I say have the event and whoever doesn't want to attend doesn't have to. Maybe you could put some feelers to get feedback on how her friends and family feel about it.
Do you think it would be easier if you take the spotlight off your aunt? You could call the get together a reunion or something like that. Your aunt would still be able to talk to and hug her nearest and dearest without having to be the center of attention. Sometimes being the honoree takes a lot of energy and she might not have much not spare. Something less formal might help guests to feel at ease too.