I was just there last month as well. If you are a Diamond or staying in a suite (not sure about other club rooms) you don't need to purchase a ticket for the Hoi An shuttle. Just call or ask in the Regency Club or front desk in advance (they say at least half hour ahead, but you can reserve earlier if you want) to reserve a spot, then show up at the scheduled time. During my stay both mornings I took the shuttle to Hoi An it was full.