That is, unless you're almost civ 5 strategy persia. Make the boom times periods of development. Just don't waste it on building wealth or research. Switch over to production focus and build other Wonders, expand your military. Make the most of it by ensuring that most tiles around you have at least 1 gold and 1 hammer so that you practically double your production and income.
The immortal isn't bad either, but the Archaemenid Legacy is where it's at with Darius. The Satrap's Court is a nice uncompromising upgrade as opposed to a regular bank. Money and happiness go hand in hand I always say. Medic is a great upgrade for them when taking out barbarians.
Darius I Civ Bonus: They also heal at double rate.