IMO, Concierge class is not worth the extra $$$ on Century, mainly due to the fact that the stateroom is exactly the same as a standard balcony. Having said that, if the canapés are worth it to you ( you must be in your room when they are delivered, at about 4pm to receive them), & having flowers & fresh fruit in your room appeals to you, then by all means go for it. HOWEVER, for $100, I would consider it! Priority boarding is practically meaningless, because you will find that when you arrive, there are so many lines,& is you are Elite due to your RCI level, there is no difference.
Please make sure that you advise Celebrity of your proper level on RCI, as they will not know otherwise! Call the Captain's Club desk @ Celebrity to advise them
Enjoy your cruise!