Thank you for the replies. I'm very interested in seeing whether something could be done to make the land-grab fair. The inspiration came from reading a cover story from National Geographic on new discoveries in China that shattered old concepts on the origin of China. Here is an exerpt:
http://magma.nationalgeographic.com/ngm/0307/feature3/
The archeologists there are challenging the old view that the Shang culture (e.g., prototypical Chinese culture) did not start from one area and spread (the Civ colonization model of empire origins). Rather, the earliest Shang city was one of many in the area that shared closely matched, but yet different cultures, that grew up parrallel to one another in the region. Gradually they were assimilated into a more cohesive group (the Civ conquest & cultural conversion models of empire origins).
Although it would be foolish to apply this accross the entire globe without evidence, there is plenty to be found when one looks for parallel origins. Among the ancient civs I am most familiar with, you can find this pattern at work in Babylon, Sumeria, Greece, Egypt, and throughout MesoAmerica. The Israelites are a glaring exception, who mostly grew out of a single nomadic group. But even they established their geographic homeland more through conquest than colonization. The same is true for early Rome, which mostly went out from a home city and conquered/assimilated surrounding cities of similar culture (I'm talking about their immediate neighbors, not Carthage and Greece, but that later development only strengthens my argument). For the most part, it seems, rising civilizations were not colonizers as much as they were conquerors and assimilators.
The problem with trying to incorporate these ideas is that it tweaks a major part of the game that is already very finely balanced, and failure mostly through destroying that balance.
I've also considered making cultural improvements off limits to these barb civs somehow, so that the regular civs aren't the ones being assimilated, but the reverse. One idea is to make a hidden, untradeable, starting tech for regular civs that allows a resource to show up on the map called "homeland." One of these would be placed under each starting location. It would be a required resource for any culture-producing improvements/wonders.