For me, it's economics as much as anything else. I really can't afford to have $1k+ bags sitting around in my closet if I'm not using them. I have one Bbag I don't use much right now because of its light color, but I know I'll use her all the time in the spring, so it's OK if she sits in the closet for a little while now.
I've given almost all of my Coach and LV bags the boot this year. I don't miss the Coach at all. I do miss 1 (ok maybe 2) of the LV, but I'd still rather have the Bbags!
I've never sold a Bbag. My resources are limited, but I live in NY where it's fairly easy to do research on what I want, so usually by the time I get something, I am very very sure that it will suit my needs.
Sounds to me like the size is a real issue. I would sell it and get something else.
As far as seller's remorse goes, I would maybe take it out for a day and see whether the size really bugs you or whether you get used to it. Then you can be REALLY sure.
And the timing, I would wait a little bit, unless you're pressed for money. Now is a slow time when everyone is buying for others, and after the holidays most people will be broke. Also, the longer you wait, the more value the color will have - as tends to happen with bags that haven't been around for a while.
I think there are at least two types of people when it comes to handbag lovers--- some only want to keep the ones they use all the time and don't like bags or other things just sitting there not getting used, then there are those like me...who don't have to use it to love and enjoy them! kind of like a collection...that you admire!