For what it's worth, and based on my own opinion of some comments on here thats probably not much.
I've owned many many HD diesel trucks over the years, everything from 6.9 Fords and 6.2 GM's to an 07 Cummins and that includes an 04 Ford 6.0. We still own the 04 6.0 and yes we put about $2,000 into it as a prevetative measure. In 8 years and 230,000 miles it's never left us stranded, never missed a beat, it starts better in the cold and pulls just as well as the Cummins which has quit on us twice. If you like the truck put the money into it and keep on truckin.