The best embellishment to buy is always the one that I know exactly how to use with the photos that need this very embellishment to make a perfect page.
I have warned about buying cute embellishments for the future. I bought my my oldest sticker set during a California trip in 2002. I still think they are adorable, and have yet to figure out how to use them.
The eureka moment occurs when I see a set that solves a problem by providing the perfect caption, title, and decoration for photos that have been waiting for inspiration. My children's Christmas pageants were a challenge. I only had one or two per year, and the photos were not great. As soon as I saw an "Away in a Manager" sticker set, I could make the page. I enlarged one little shepherd, cut out her cluttered background, stacked the other three photos, and used the stickers to tie them together. The best sticker set ever !