Is it (still) a good idea to take a taxi from Don Meuang airport at arrival level, to avoid queues from departure level?

You had this mixed up right? Think about it,,,,

 

The answer is yes, though you will have obviously done the trip well before now.  Avoid the queues (& surcharge) at the official taxi stand at arrival level by proceeding up to the dep level and grab a taxi that has just dropped off someone.

Saves the driver a very long wait (sometimes 1-2 hrs) and you a queue....