There is some truth in Dee's accusation, but not as much as she believes. "Everyday Use" is an excellent study in family dynamics. Dee has gone to live in the 'big city' and is much more aware of what is going on in the outside world than her mother and sister are. Both Dee's mother and sister value their heritage, but their views are colored by the experiences that they have had, as opposed to the material value that an outsider would place on those items.
The quilts are a perfect example of this. Dee has recently decided that she wants the quilts, items that she once rejected as being old fashioned. Dee wants them because of the value that society places upon them, that of a material sort. That's the type of "heritage" that Dee has become an expert on. Dee's sister, Maggie, wants the quilts because of the memories that she associates with them. She values her heritage in a much deeper way than Dee does because she connects emotionally and genuinely with her family and ancestry.
Mama, the narrator throughout the story, realizes this and tips off the reader in subtle and not-quite-so-subtle ways throughout the text. Dee's consistently described as smug, an outsider, and abrasive. Quite frankly, she's really dislikable. These qualities serve as a way to highlight to the reader how little Dee really does value her heritage; it's simply another superficial thing to her, something that will change if it falls out of style.