I think I get what you mean, and I think we all do that to some degree or another. I think it is just more of a priorities thing. Some people like to splurge in certain ways that makes them feel better, while splurging $ on this or that other item just don't give the same feeling, so it FEELS more like a waste.
I coupon at the grocery store (and anywhere else I can, lol) and try to make reasonable cost efficient choices about food. But we eat out a lot. I KNOW I could "save" $150 a month just by cutting back on our meals out away from home... but we value the lack of stress and time that would go come along with the alternative more than that $150. I don't save $150 in coupons at the grocery store every month (to cover the expense of eating out), but if I was blowing money hand over fist at the grocery store it would just compound the problem and I'd feel badly that I was "wasting" money when I could save it easily. It doesn't affect my feelings about grocery shopping to use coupons, in fact, it makes me feel better that I am trying to save $ for our family. But eating out helps me be a better mom/wife in other ways sometimes and cutting out that expense from our monthly budget would not "buy" me $150 worth of stress free family time.
Does that make sense? Now, I just used the grocery store/eating out example because that is one of MY things. But you could apply it to others and their "things" too, like your friend with the airfare and luggage cart. She probably LOVES flying and travel, but abhors paying for something she can do herself so easily.
And if handbags are your thing, then you probably get a much bigger "bang" for your buck when you spend $ on one of those, rather than on a cheaper one. If you get that big of a thrill/that much enjoyment out of designer bags, and you can afford it, then enjoy! There really isn't anything "foolish" about knowing what sort of spending "speaks" to you. Now, if you don't give a hoot about handbags and just want something that does the job, then spending $500 on a designer one and clipping coupons for groceries would seem odd.
We all have our "things". ;)