The heart wants what the heart wants. I sold auto parts and accessories for 20 years and I can say there was very little rational thought when buying accessories and speed/racing parts. Let us say that many purchases were motivated by glands other than the brain. I've said that fishing tackle is designed to catch fishermen more than fish. And so on.
Certainly there are other factors than cost per ounce, but it may clarify a purchase or get past what I call the "sweaty palms" stage of making a decision. There's not a lot to consider in buying an 89 cent spork, but I'll bet there are people out there who feel they can't afford to lighten up and/or are paralized by the process. In some cases, they feel they are betting their safety in the purchase too.
We read of sub 5 pound kits and drool over light gear that may have more worth in its light weight than being appropriate to our personal use. We have a lot of hiking disciplines in the UL niche, with adventure racing, thru-hikers and weekend warriors all dipping from the same suppliers.
My example of the stuff sacks was just the one at hand. If you look at sleeping bags, I have a typical 48oz synthetic bag that is good to, let's say, 25 degrees. Now, I would want to get lighter and improve on the performance if I can. A Western Mountaineering 20F down bag is 26oz @ $315.00 or $14.31 per ounce --- on the weight savings. There's some decision making in going with down over the polyester fill too. If we were to compare two similar bags then we could do a simple apples-and-apples comparison, say a 28oz bag at $300 vs. a 26oz bag @ $350-- do you want to gain 2 ounces for $50?
If you go through your gear this way, you will find a few things that will pop out. A pair of REI midweight long johns are 9oz and I didn't need the extra insulation and could go for a pair of Patagonia Capilene silk weights at 6oz for $24. I saved 3oz and got gear closer to my needs for $8 per ounce. It's a little easier to deal with $24 changes in my gear than $315 changes. You can see that I made headway for $8/oz vs. $14.31/oz with the sleeping bag change. Money aside, we would LIKE to do both!
These comparisons could be mitigated by selling or trading the old gear, which I do a lot of. I could trade in the sleeping bag with one supplier I deal with, or sell it on Ebay or via Craig's List, or trade with a friend-- or here at BPL too.
You could look at volume the same way. When I switched from a plastic trowel to a tent stake for digging cat holes, I saved an ounce @ $3.95 and made little more room in my bag. 10 points for the Rambo factor too-- Yo! I dig holes with a tent stake and eat bark for breakfast :)