Your bicep does two things:
1. Supinate the forearm
2. Flex the arm along a fixed plane
The only real variation one can add to a bicep exercise is to increase the degree of stretch at the bottom (incline curls), or to pronate the hand. You don't really need to do either to have a fully developed bicep; doing all variations in one workout won't aid with development. In any given exercise, the biceps bear the full load, so why bother doing 15 different bicep exercises? It's all the same.
-casualbb