New coins give those not on the inside at least a chance to make profit. If all we have are 2 or 3 out of a thousand old coins that will pump that week, well, I'm out. That is truly throwing darts at a board, I'd rather play blackjack or the rulette wheel.
That's a daily chart of ALT100USD, an altcoin market index based on value of 100 coins, being traded on Cryptsy. A value is calculated in USD.
You can see that the minimum was 25.139 (Jan 2015) and a current value is 58.65. (+131 %)
So you simply could buy all index components not guessing which coins to choose and have a good profit of the whole portfolio.
Why Cryptsy coins? Because Cryptsy never delists coins (one exception was LGD which was a real scam with an exploit).
Why old coins? 1) not to deal with numerous scam ninja coins and not time-tested one 2) because the pioneers, released before altcoin big bang in 2014, have a value of collectibles, at least.
With a current value of 58.65 ALT100usd still doesn't seem to be overbought. That index was first calculated on January 6, 2014, with a base value of 1000.
It seems since Jan 2015 there is an up trend and probably 1st wave has ended in April.