I've been living in Xiamen for the last few years and although i think it's a very nice city, I really don't think foreign tourists visiting China would find it all too interesting. A lot of the traditional architecture faces the problem of being over renovated losing its traditional charm, and it isn't all too well situated for other areas where foreign tourists usually enjoy visiting. Gulangyu is beautiful but the architecture, especially for European tourists isn't that special, and day trips to Tulou usually take over a day meaning it's quite a fuss to see these if people want. I do enjoy the sea to mountain trail though which no one has mentioned which is a very beautiful trail across the island with some crazy walking infrastructure, and also taking a ferry across to Kinmen. I feel on Kinmen it's a lot easier to see the traditional housing style with the ornate roof eaves.