What are the advantages of 1.8 rockers?

The 1.8 rockers increase valve lift to a higher degree then the 1.7 rockers. This allows the engine to breath easier resulting in power gains. Therefore you will receive greater power gains with the 1.8 rockers. However due to the valve guide machining requirements of these rockers, the price of machining far outweighs the performance benefit of these rockers.