Well concentration is just being able to focus on something, in this case the breath. If you can't focus then your mind wanders for a long time, meaning mindfulness doesn't get used very often. As far as lucidity goes, I suppose being able to concentrate would help to stabilise a dream and maintain lucidity (I have read people reporting that they lose lucidity part way through a dream sometimes, I have never had this problem so I don't know) but I imagine concentration would help with that. Also being able to focus would mean not falling asleep during WILD for example. Lots of things!

I think it might take forever to list all the things a powerful mind could be useful for. ;]