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

It actually depends on what you are holding. There are altcoins that are worth holding and there are some that are just good for just a short term hold. Not all altcoins survive after a successful ICO, even ICOs who have gathered a lot of funds die too soon due to poor development and marketing strategy. Just make sure to be updated whether if the team is active.