Its quite hard to ensure profits from airdrops. They wether don’t pay or if they pay the tokens doesn't worth much. So for me its a waste of time.
But not all the time. Many airdrops are paying much higher than before so if anyone wanna give it a try there is no loss go ahead for 10/12 airdrops if you earn some $ then keep doing.
I'm afraid that won't be enough. Since you yourself said AirDrops either pay little or their coins are worthless. Therefore, it is important to understand that out of 100 projects, only a few will be worth something. This means only one thing that you have to participate in as many AirDrops as you can. Provided that you decide to participate in them at all. Otherwise, a situation may happen in which you missed one or two projects, namely these projects paid good money to their participants.