My 13-year-old Garmin eTrex Summit, while slower to get a fix and with less battery life than newer units, continues to impress me with its ridiculous ruggedness and longevity. If your existing unit continues to meet your needs, it's hard for me to advocate replacing it.

For others reading this: As always, make sure that you have non-electronic backups that you know how to use. I don't get out as much as I'd like to, so I set important waypoints in my GPS but otherwise don't use it other than spot checks. This helps me keep my map, compass and observation skills from degrading.