I'm watching this as well. I think people move to lower cost high volatility coins in between the major pumps Ethereum does. If Ethereuem moves x percent they quickly move out of the tertiary AltCoins and into Ethereum. Once Ethereum stabilizes they diversify their portfolio.
This is a strong strategy for the very reason we all believe the entire market is undervalued. For instance if Siacoin is much more likely to see a 200% rise in the course of a week than Ethereum will so it would be a good strategy to keep a few thousand coins there.
What are your thoughts? Any AltCoins you are really fond of?
RE: Which kind of correlation is there between BTC, ETH and altcoins/ERC20 tokens?