How exactly do altcoins gain value? There are so many altcoins out there and honestly you can see connection among these in terms of the drop and rise of price.
Alternate coins usually have different properties from bitcoin, for example XMR privacy, ETH dapps, SIA storage.. etc etc
It solves different problem than bitcoin does
But IMO altcoin will always "pegged" to bitcoin because majority of exchange pair altcoin with BTC