Altcoins are like penny stocks. They can rise significantly or go to zero. So, buy altcoins or not depends on your risk tolerance.
It depends which altcoin you use.
The bigger ones are less volatile then the smaller ones, but they are more volatile then bitcoin.
Personally I prefer ETH, LTC, DASH but there are more promissing coins.
But some advice:
1) Don't invest money you can't loose
2) Diversify, both within crypto as outside