I'm interested in the priciples behind this discussion. I do think what the OP is talking about factoring in what YOU will REALLY WEAR IN 1 SEASON and what you already have in your closet important to consider. Unlike many of the ladies on the thread, I'm coming from the perspective of someone who regularly wears wardrobe items out and is looking to expand my wardrobe in the future because my current wardrobe is TOO SMALL for my current needs.
Instead of trying to figure out all kinds of math and find magic numbers for CPW or numbers of items in my wardrobe I tend to take a different approach (and this could be because while I have an analytical side, I am not math-minded). I like to wear my stuff out and use it before it dates, but I also have a widely varied lifestyle and need lots of seperate occasional clothing, which would kill a cost-per-wear, and never get figured into a hanger-turning or "x" number of items system properly.
I recently bought 2 pair of dress slacks . . . one a seasonless black, another a dark wool. I also have a black pencil. With my lifestyle I will probably only wear each pair of slacks a handful of times a year, but I also know that I will need them (have already worn each several times) and if they last as well as my last pair I will wear the black pair for 5-7 years. The wool are worth having in my climate so I don't freeze at winter funerals and work events. The pencil is more dressy, better for hot weather, and can be paired with other things to wear going out or to party events. Same with my button downs. On the other hand I am going to wear through my jeans and tees like lightening. In a third category I still need dressier tops, accessories, bottoms for my non-dominant seasons, and toppers which will all get worn less than my tees and jeans but more than the buisness clothes, but are essential to making my wardrobe work for me and my crazy life.
Instead, I think the key for me is mindfulness. When I am looking at a piece of clothing online or in the store it goes something like this:
Do I really need this? What do I already have like this? Would it replace that because this one is better in X way? Do I wear the other enough that I could see myself wearing this frequently as well to break up the wear? Does it fill a hole in an outfit or for a situation I've found myself with nothing to wear for? Could or will I wear it to work? How am I doing on the amount of work clothes? Could or will I wear it with the SO on weekends? How am I doing on amount of clothes for that? Are they getting used? Do I enjoy them? How is this the same or different? What kind of weather will it work for? Will I want to wear it next year?
And also . . .
Do I really love this? Do I love it enough to wear it regardless? Do I love it enough to get rid of something else in my closet? Is it a trend I wanted to try out? Does it speak to my style persona or where it is heading? Is it a good color for me? Do I want this more than I want something else I've been saving for or had my eye on or like to do?
For me most often there are two questions that impact my shopping---
Do I really need this?
Do I want this more than I want something else I've been saving for/like to do?
Of course, I do apply those questions liberally. I determine need based on replacing frequently worn items, on making sure I don't have to do laundry more than works for me, for having enough outfits for all the roles and events in my life for multiple seasons, and even for things like being able to rotate out shoes during seasons where I wear the same type of shoe everyday. I also am not super strict on the second question and will spend money on an item that I may not want as much as I want the vacation I'm saving for and I try to earmark fashion funds-- mostly just because although I love clothes . . . vacations, education, and certain other hobbies will win out and I would run around naked! Still, that question really stops impulse purchasing.