I'm fascinated by the change in popularity of different attachments over time. Like the tucker, which was one of the earliest attachments, and it went out of favor in the mid 40's and after that, was no longer included in the "basic" set of attachments.
The Hemstitcher is another that was rather popular early on - and then slowly went out of favor.
I do plan on learning how to use all of the attachments, once I have a bit more elbow room.
My biggest problem is falling in love with very early attachments, when I really wanted to stick with about 1890 and later. But then I know a guy who will take any "early" attachments I can unattach myself from LOL!!