I would highly recommend avoiding alt-coins. And it would not spread the risk to buy multiple alts since they are all based on the same technology. Want to diversify? Buy some bitcoin, gold, real estate, stocks, etc.
It's right that most of the altcoins are based on the same platform. I think that the crypto diversification is more about securing oneself against this if one of the coins fails for various reasons. Then there are others that can give you a profit.
Divertions is really needed especially with the market like this, fluctuations are hard to predict if you will invest in only one project and if things won't go to your directions then you are going to lose bigger part of your money while if you have a good plan and divirt your money in another project chances to recover or earned a little is possible.