Living up in the Northeast, I've had to replace both hard and soft brake
lines on my '97. Didn't do that 'til they failed. I was lucky there was no accidents and certainly don't recommend doing it that way.
Depending on where you live, and the harshness that the weather has on your truck, I would inspect and have it done before trouble happens. If you invest in a good hydraulic brake flaring tool and choose better brake line material, you can do it yourself and save as much as 1,500 bucks.
With the '05 that I now have, I've already had to repair the push in transmission cooler lines that rusted at the 90° bend coming out the radiator. Could have lost my transmission fluid in a truck that only had 65K miles at the time. Really disappointed in the poor materials used on these vehicles that can lead to catastrophic failure. Maybe Ford and other companies assume that you should just move to more favorable climates if you want your truck to last. I don't think living up in north east NY can be as bad as Siberia.