I just did a quick audit.
I own 9.
2 are "party" dresses —one an all-year round LBD that is a bit on the subtly glamorous/sexy side, and one is a very light silk chiffon going-to-a-wedding-or-garden-party type dress, suitable for warm days only, even with a jacket.
2 are all-year-round sleeveless jersey sheaths that can be layered over or under, one black and one blue-grey.
1 is a multicoloured midi sheath that works best in spring/summer/early fall.
1 is a multicoloured midi that works only in late fall/ winter.
2 are sweater dresses, one for fall/winter and one for spring.
1 is a turtelneck sleeved dress in a light fabric that can be layered over or worn as is. Good for spring/fall/winter (but not winter's coldest days).
Practically speaking that means I have about 5 in each season, with the addition of a dressier piece. I think for me that's a pretty good number. But I will probably add a sundress for summer if I can find one I like.
I get the impression that you love shopping and buying. So why not just weed out the ones that no longer thrill you, either by selling or giving away, and make room for more shopping adventures!