Snorkels are great at one thing.
Stopping water ingestion.
Down side is:
Your air filter will become dirtier much faster, requiring either more cleaning or replacement more often. Believe it or not, but where the air is taken from factory is unbelievably good at preventing most of the crap getting into the air box.
Intake restriction due to the amount of bends in it, and the length of the pipework.
In any turbo car, the real measure of oxygen is not what the air temp is hitting the turbo.
Its how good your intercooler can work.
Dropping the intake temp at the turbo inlet by 20deg, does not mean your post intercooler temp will drop 20deg...
On a naturally aspirated engine, that 20-30deg cooler air would make a hell of a difference to power and economy even with the intake restriction. So if you owned a v6 petrol, I would say it could be a performance gain.