Many ICOs have their token sold at a fixed price vs. the ETH. For example: 1 ETH = 1000 Tokens.
So does it really matter if the prices of ETH/BTC is dropping?
If anything, then buying now you get more Tokens for the $, right?
I do not think it is the best time to invest in ICOs. It is rather difficult to collect a Hardcap on the current market. Personally, I prefer buying ICO tokens on exchanges because they usually cost lower than during ICO.