Carter, this makes perfect sense to me. You're in a similar position to where I was at the start of this season. I had finally replaced/ upgraded enough that I had a working closet. But I still needed the "glue" pieces and some statements to make the wardrobe really sing.
I'm still in the process of figuring this out for myself. But in my experience, footwear can be huge, and, as Angie says, finding a couple of key trends that you want to play with. That might not be true for those who do not have a modern classic style, but it is particularly important for those of us whose core style is modern classic. Otherwise the "modern" disappears from the "classic" awfully fast.
To determine my true needs, I am doing what Caro has suggested in the past -- keeping a strict tally of what I am actually wearing. I am going to do this for the season and then re-evaluate the size and distribution of my closet.
I don't think I can follow any strict "numbers" system either -- whether that be a 10 item wardrobe, a 333, a 37 item capsule, or a decision to purchase 6 (or 10) items per season. It just ends up feeling arbitrary and silly to me, somehow. I do have limited space in my closet, and so I simply work with the space I have. I can't have more stuff than I have space for. My fashion budget is about to get a drastic cut, so that is also going to be an issue in future.
But once I have a very clear idea of how many wears each type of item is getting, I can decide more easily on whether I really want or need to add any more of that type of thing to my closet. Or whether I want to edit. Or simply upgrade what I already have. Or get rid of a few of "those" in favour of a few more of "these." Where do I get my biggest joy for the $$?
I DO think that focusing on creating 6 fantastic "10" outfits is a great way to go. And you can look back at some of last year's outfits now and ask yourself -- what would have made that a truly fabulous outfit, to me?
We always do a post around New Year's, collecting up our favourite outfits of the year. That can be a great opportunity to review your style and to see what might be missing.