Case in point, we just used some EMS 30 degree down bags that are 25 years old to spend New Years on a 5 degrees F mountain.
(Zipped together with a 15 degree 800 fill used inside as a quilt). They aren't anything special, and I doubt that they have better than 600 fill. However, they've been extremely useful, and proper care has made them have a long and productive life.
Same for a 35 year old T-rest pad CCF that has never leaked, despite hundreds of nights. We take care of gear when we get home from a trip, but more importantly for us, we take care of stuff on the trail. Extra precautions for keeping dirt/snow out of the tent, policing sharp objects, trying to pack stuff in a protective manner, and just having an attitude of taking care of gear so it takes care of you, really helps us keep the gear that works . Though we've shed many pounds off our backs with new purchases and I would love to spend thousands we don't have on newer gear, I still can't bring myself to jettison durable stuff sacks to save some ounces. Sil-nylon has replaced cordura, but they still get used.