I had a 7750 that lasted 3 years, including a dunk in a mud puddle. I imagine that if you keep it up to date, etc, it should last you that no problem. I would agree that you would want to buy the latest possible device to give it maximum utility, but I would think that you could do this with no problems.
You might want to buy a new battery about halfway through, but that is a nominal compared to the cost of a device.
"out of chaos comes opportunity"