Some things that are significant about this book (in my view) that were not mentioned in the SparkNote are this:
Billy Pilgrim's last name
A religious connection in the book
The colour of his feet again
As to the first, I think that since 'Billy' was obviously chosen with care, 'Pilgrim' was too. Pilgrim could refer to his otherworldly journey through time, although it's uncertain what he would be making a pilgrimage too - possibly death. Or, it could just be his journey through the war.
As to the religious implications, Christianity is only mentioned once or twice, but I think it's worth mentioning. When Billy is in the train car, he has to sleep standing up because he moves in his sleep, so he braces himself against the corner of the car by putting his arms out, "self-crucified." Billy does have a slightly Jesus-like demeanor in that he is mild and subservient, although he is following the whims of time, not God. Kilgore Trout also wrote a book about somebody who went back in time to find out if Jesus really did die on the cross (he did) and measured his height (but not his weight). Vonnegut also says that Jesus, at age 12, while learning carpentry, helped build a gallows for a criminal of some sort, who was executed. So it goes. I'm not sure what to make of that one.
Finally, the blue-and-ivory thing, although it is mentioned at the beginning of the book, only first occurs on Billy Pilgrim's personal linear timeline after the bombing of Dresden. It's possible that this means that Billy was actually killed at Dresden, not in body, but in mind.
Oh, and let's not forget the irony of being saved by being in a slaughterhouse.