Yep, you can duplicate them but in code terms only seven can exist. And of course it is possible to simulate them with resources and buildings (I call these Marvels so as to distinguish), even throwing in faction capability for faction-wide bonuses. These can be indestructible or simulate a seize-secure-exploit development of blgds which give progressively better bonuses. You can do that for real wonders too, as I have in FATW.