Since I was so close to getting all the achievements in the game, I went back and, er, got all the achievements. Collecting all the feathers was the real time consumer, especially since I only had 30 or so of the 100, and after that I just had to wear my prize in all the game locations (easy) and perform a few fancy fighting moves for the remaining achievements.
And that’s it! I could go and get all the treasures now, but I get nothing for it (except money, which I have more than I could ever spend anyway), but I’ve done everything else!
Brotherhood needs to be bought now. And soon. I did buy it from the online Ubisoft store, but they cancelled my order, so I hate them now.