Most of the altcoins start with a crowdfunding and with investing (ICO) at most of these funds are accumulated in bitcoin.
By this not only that these altcoins become popular but also bitcoin become more popular because through bitcoin they are investing in another cryptocurrency.
Indeed. Maybe doubling bitcoin could be possible in investing with altcoins. They have been looking for a way to double it, it might not be that fast but it could happen if the invested alt will really shine.
I haven't invested in any ICO but it contains the risk, because the price after the ico can drop and you can lose.
But also it is a good opportunity to make a profit, I saw many coins that their exchange rate was way to high than the ICO price.
You should not wait for long after the ICO finishes because after some time the price would probably drop again but at the moment when ICO finishes the price is always higher then what it was while ICO was running so if you sell them on the right time you can make some good profit with it.