Rhye, seeing as there were never THAT many colonial empires on Earth* you can make a set of wonders named "First Colonial Empire", "Second Colonial Empire", etc, totalling at say, 8 or 10 such wonders, each one costing a bit more than the one before it, all having he exact same effects except the first three having one more culture than the rest. They would all be enabled by an optional tech called Imperialism. Basically whoever starts work on their Colonial Empire will have a better Empire in some ways and only a limited number of civs could ever get such an empire. You can also make these wonders require some resource available only in Africa, NE Asia, and the Americas (all in specific sites where early colonies were built by the colonial powers,) only visible with Imperialism, and then only someone who already started colonizing will be able to get it. Maybe this idea is a bit too complex for the regular game, but I'm sure you could fit it into the Xpack. *In game terms we'd have France, England, Rome, Spain, Portugal, Netherlands, and perhaps another one or two that I may be forgetting.