thedseer, to be honest, I stopped thinking about the 'versatility' of my collection, and about collecting in general. I stopped trying to have a handbag for every occasion and to fit every function.
I love the idea of a crossbody, and it's very useful, but I get tired of carrying them. I want to be able to throw it over my shoulder. So any *only* crossbody bags are out. A hobo or a shoulder tote with a crossbody option is definitely in, though.
It has to be able to fit under my arm without making my arm jut out. So nothing wider than 4" deep. I think that E/W bags make me look fat (lol) so I go for square or N/S only. Even though purple is my favorite color (tied with red), it's too limiting in my wardrobe because I do wear a lot of red also. No flaps, they're annoying. No clasps, they're annoying. Hardware can't be too loud. Must have enough pockets for my cell phone, keycard, and candies. Strap drop can't be too short and in my armpit. Flat straps are better than rolled handles. Can't be so big that my stuff moves around.
So basically, I get rid of anything that has anything I can complain about.

Even if I love the leather, the look, it fulfills a certain function that will be empty if I get rid of it.
What's left? RM wine mini nikki w/ brass hw, because my favorite color combo ever is wine, navy, and brown. And it's just the right size, maybe a tad small. Kind of a pain for everyday use though. HH oyster lorca: yes it has a flap and a clasp, but I adore this leather beyond belief and I won't get any resale value out of it.
Coach black ergo hobo: my first designer purse, rainy day bag, also no resale value.
I've gotten rid of multiples of just about every RM style: Nikkis, MAMs, mini beloveds, mini matinee, full size matinee, MACs, couple different HH, one BE, couple coaches, one MbMJ. It has taken A LOT of buying and reselling to figure out what details work and don't work for me. And a lot of thinking, lol.
Clearly the HH and coach aren't perfect but also aren't going anywhere, so it's really just the RM that is my 'collection'. And it's not the perfect bag for me either. I think I need to add a brown bag, a tote with a crossbody option would be great. There are occasions where I do find myself needing something, well, bigger and not red. I'm thinking about the LP dyan, or the Bella small tote. I am also drooling over the Bal town, maybe in the sometime distant future when I am employed again.
Well now that I've finished my novel, I hope that helps!