'Heirloom quilt', as I've seen the term used most often, refers to a quilt that is special in terms of the skill/artistry/amount of work it represents, such that one can imagine it being handled with care and passed on through generations. I don't think it necessarily implies that it must be shut away and not enjoyed. Having said that, an heirloom is not necessarily something objectively valuable; the value could be sentimental, and so any quilt made by someone that was greatly loved within the family could become a family heirloom.