Ha! I don't think I am an average shopper. The way I have been buying in the last two years, I feel like an EXTREME shopper!
Keep in mind, though, I was truly wardrobe building, not maintaining. I started YLF with literally NOTHING. Not even underpants that fit. And had no clear idea of my style...which meant a lot of experimenting and tossing, you know?
Sigh....(thinking of the money I have spent on all this....)
I also tend to buy for an entire season more or less at once. And then not shop for several months at all. That's why something like "Austerity August" is actually no challenge for me. It fits with my usual pattern. A real challenge for me would be to "make" myself buy one, two, or even three items a month. It's not the amount so much. it's that I want to shop when I want to shop, and don't want to shop when I'm not shopping. If that makes sense.
I definitely bought more than 3 items a month this spring, on average! I think I bought more this spring than I have bought in my entire life.
I haven't yet figured out what a reasonable number of refreshers per year might be. I am sure it would be different for each person. I know Angie allows herself quite a few if she likes the offerings, but she needs to look especially on trend and up to date (and would want to, anyway, I expect, given her style). I know she also cuts back in seasons where nothing tickles her fancy.
And of course some would depend on wear patterns. If you wear your clothes out, well -- you're going to need to replace them. Of the things I wear frequently, some of them actually DO wear out. I must be pretty hard on footwear -- I go through at least one pair of sandals a year. I mean wear them into the ground. Ditto for booties -- I usually have a favourite and that one will be worn to bits by the next season.
Anyway -- this fall should complete the real "building" phase of my wardrobe. After that, I think I'll have a clearer sense of what a moderate upgrade pattern might be. I do think your average of 3 items a month sounds pretty good. It would allow a person to get 6 items per "sub-season" -- which makes sense to me.