Over on Ramforum.com the Ecodiesel is a mixed bag. Some people no problems. Some people...9 months in the shop, full engine replacement and more.
You may get better mileage but there is a higher initial cost and much higher maintenance costs. Just a guess...you'd be looking at 3-4 years to make up the difference (in gas costs).
Its personal preference. If it was me I wouldn't buy one. If I was going to buy a diesel I'd get a 2500 with the Cummins. But thats me. Its your money...spend it the way you want.
If you're really looking for better mileage you'd be best off with the Pentastar V-6 in a regular 1500 (Bighorn/Laramie, etc). That is a great engine, great mileage (25-27+) on the highway and reasonable power (300hp) along with lower costs. If you're not doing much towing get the 3.21 gears and you're mileage will be near the Ecodiesel....and a huge cost savings.
One thing....if you do buy one...do NOT go without a full extended warranty. You'll want the entire engine covered for 100K miles at the minimum.
Good luck with your choice!