I think Alicorn's intended point was closer to "How will owning this item change my preferences and my habits? Do I want my preferences and habits to be changed in this way?" (Sometimes the answer is "Yes!")" than "self-modifying into someone who likes to make muffins just because I bought a muffin tin." You need to do the value-weighing before you purchase something.

Also, she's made an underlying assumption that a) you have limited resources, such that buying something is a tradeoff against buying something else, and b) having stuff you don't use creates "clutter" which is unpleasant. These points may not be true for everyone: someone making $150,000 a year probably doesn't have to ponder very hard on whether or not buying a muffin tin is worth it, because it has a negligible effect on their savings, and not everyone finds having a lot of stuff distressing. I do think it's true that most people err on the side of buying too much (see rising Canadian household debt) and keeping too much stuff around.