As far as the exchanges go I believe alt coins give you the potential to earn more money quicker but with a bit more risk. Obviously you can just hold btc , buy low, hold repeat but alt coins tend to be a bit sporadic and you can make a bigger profit since they are cheaper and mostly directly correlate with the current price of BTC. As far as surpassing in the usefulness aspect, there are some promising alt coins out there with their own purpose but I don't really see anything replacing bitcoin in the near future.