I dunno, but 5-6 sounds low for me if trying to update and clear out some cobwebs. "Maybe next year"...! I could buy 5-6 items or more every month if you count every type of clothing category and it not be too much if they are all put to good use and some replace other items.
However, I think I am getting better at thinking in terms of seasonal and style refresher/updates, which overall should be fewer items but more intentional--not buying 4 or 5 new tops out of boredom because I'm not focused, or more of the same pants. So the number is less important than the plan. I bought fewer items this past quarter because I was shopping for ideas and buying for the plan (somewhat--not perfect!).
Quality is important and I know it's the key buzzword, but I've actually learned that the style of the shoe or garment is equally important . I had been buying some good quality (though not bespoke, or whatever) items with a relatively low style and happiness quotient. The 2 concepts overlap, of course.
This fall I bought a pencil skirt that I love and that goes with virtually everthing in my closet (well, not quite). Also re-surfaced one that looks good now with updated items. And I have a 3rd that is pretty good. So I'm trying to realize, okay, pencil skirts are great, but WEAR THESE every 2 weeks (or so, depending on work schedule) with different tops & shoes that look on point, make them earn their keep, for the next year, and don't go looking for the next new pencil skirt just to have more. So I also look for categories now I should "let rest" for the next few seasons or so, as more of same would not change my style or fun quotient. Later on I will need and want to replace them.