Hi Aesqe! Nice work. I've tried the plugin before. I think the main issue I had was that it was a bit complicated to navigate/make sense of.
What I'm envisioning, is much simpler. A top level menu item called Galleries. Inside is a tabular view, just like Posts and Pages, with a list of all Galleries. The process of creating a gallery would be three simple steps:
1) Click "Add new gallery."
2) The interface is simply two panels; on the left is a list of all items in the Media Library, on the right, a blank panel into which you drag items to build the gallery (order can be changed with simple drag and drop, items removed by clicking a delete button beside the item name).
3) Hit save.
Then, within a page or post, there would be a meta-box called "Galleries," with a drop-down allowing you to select the gallery (or galleries) you want to include. Of course, all titles, descriptions, and captions would be taken from the Items themselves.
Having to worry about attachments, copying from one post to another... it's confusing for the average, non-programmer minded user.
Take something like iPhoto, or iTunes; you simply create an Album or Playlist, drag and drop whatever photos or songs you want to include; that's it. That's the level of simplicity a feature like this needs to have (and which WordPress, on the whole, does have).
As it stands WP's media management, in general, is a bit of a mess; four tiny buttons, which actually all do the same thing. Text fields on top of text fields. Buttons on top of buttons. It's not very intuitive, and I think having a simple Gallery module, as part of the core, will help. Again, it seems like a a feature that the average person would expect to see.