I really like the idea of regionalizing resources to emphasize the importance of trade, but there's something about the AI that puts limits on doing this effectively. I noticed when I play my map 'Eurocentric Earth', The AI will only actively utilize around 3 of each resource. The only time they will use more is if they were going to build a road there anyway, otherwise, they just sit in the civs territory with no roads going to it. I would advise mapmakers to give each resource four different regions or so.