I only buy new stuff out of necessity or if it's a significant improvement over what I have and makes my life better in some way. For example I've recently discovered that there are far better flashlights around than Maglites. I don't really need new flashlights but I've invested in some Gerber and Fenix lights that are just amazing for such a small package.
With only a few exceptions, camping gear really doesn't change all that much over time. I'm looking at getting a new Coleman dual fuel lantern soon, and it's amazing to look at the new ones and the old ones on ebay and there's not much of a difference.
Just for fun I was looking at new sleeping pads recently. It's amazing, my 20-year-old RidgeRest looks exactly like the new ones. Zero difference. Even the fancier stuff, the inflatable pads, etc., no difference between today's models and those from 15-20 years ago.
So unless something is seriously past it's usable days, damaged, or otherwise just not fit for use, I don't see the need to replace much.
Another example, I'm in the market for a new tent, to accommodate my son who will now be joining us on trips. And also to handle any other additions to the family in the coming years. If I didn't have that need for a bigger tent, I wouldn't be buying one. My 4-person Eureka is just fine otherwise.
Lastly, I think a lot of my mentality about gear replacement and longevity is based in taking good care of stuff. I think that came from the old Boy Scout days, where we had to be mindful of every piece of gear, knowing that there was never a lot of money around to replace things and we had to make stuff last.