If you stand up and be counted from time to time you may get yourself knocked down. But remember this: A man flattened by an opponent can get up again. A man flattened by conformity stays down for good.
I do think sometimes there's danger in guest appearance mania. I've seen too many examples that sound cool on paper like 'Oh get that guy to sing the hook on that guy's song ' and then that's all it is. It's a cool idea that sounds good on paper.