Just like Sardo said having no cooldown as a premium member will destroy the server's economy from Poison marbles to Fear Gems to Weapon socket enhancers.
If you want to farm like a madman you can make 2-3 account with the same class you're playing on your main and farm the dungeon back-to-back-to-back having virtually 2-3 minutes downtime for having to switch all your gear around each character.
And before anyone jumps on the last piece of note I wrote above, it's not abusing any kind of system it's just called being efficient.
The premium members could use some extra features, but having the cooldown removed is not one I wish to be implemented.
Cheers!