I was looking at ETH and as far as I understand, this coin is mainly successful because of the ICO's nowadays.
ICO's are booming and it looks like it never ends. But what if all ideas are gone and the amount of new coins which use/ need ETH are decreasing. Would this have much effect on the price?
Maybe someone can correct me if I am wrong?
Yes it's true and ICO's are one of the major reasons why ETH sits atop next to BITCOIN. Since only few ICO's are asking your bitcoin address rather than asking your ETH address whenever you join any campaigns from a bounty means a significant push to ETH's market value.