Last year alts rise a lot. I dont know the average percentage. But when I check coins in the market at year 2013 lots of them dead now (too low ranks). probably new tech coins won them (like peercoin, namecoin, ixcoin etc)
Also we are following new ICO s and most of us expecting too much gain from new coins which are not at the market. If our ICO expectations will happen, when they added to market, current market coins will go down. kind of paradox
I think that if a coin or token has a real application then they will not go down with the appearance of competitors. The market is very large and the projects are very small, there is enough space for everyone.