I think that participating in an airdrop with a micro-payment (like .001 ETH) is not a bad idea, since it's such a low investment/risk, and those coins, once you have them in your wallet, aren't going anyway - who knows what will happen in the future?  You really don't know - I'm sure that 99% of the ICO's nowadays will end up nowhere, but all it takes is one DASH, so I think the spaghetti against the wall approach works in this case.

And traditional airdrops (which do not carry a cost) are also a good idea, I think, if you have the time to participate.

When you are saying you are worried - I think you should stop worrying about it and accept that 99% will end up being worthless.  And go for it - broaden and do as many as look halfway decent, and play the odds.