In my hot opinion treasure hunting has been the most fun in all games where it's possible, especially in Ultima Online. The new treasure chests introduced in Cataclysm contain valuables everytime. No more moldy bananas and a few copper coins! Why not make use of it?
Personally I like the high level chests because level 80-85 rare items can sell for even
2000g a piece, depending on how good the item is and also it's availability. On the otherhand Northrend chests are worth
500g at max, and out of a Classic chest I've found no item worth more than
300g ish. But, Cataclysm zones are more crowded than other zones so finding a chest there is a lot more unlikely.
Note that it's extremely hard to find a treasure chest in the new zones, especially if you're playing during peak hours. Treasure hunting is recommended for early morning or late at night when most players are offline.
To ease your search, I recommend you to download
Gathermate2,
Gathermate2_data and
Routes addons. Gatermate shows the treasure chests on your maps and with routes you can create a nice route that connects all chests it knows of, minimizing your time spent searching for the chests.
Here's examples how it will look.
Mount Hyjal
Deepholm
Uldum
Twilight Highlands
Tip: I've seen no more than one chest per zone in Cataclysm zones.
