I am also in the pre-wash school of thought, especially with older fabrics or those from unknown sources. If it holds up well after a good wash in hot water (no major bleeding, uneven shrinkage, developing holes, excessing fraying, etc.) and the overall look and feel of the fabric after pressing seems 'normal', then I would go ahead and use it in a project. If not, just donate it and get it out of your stash. Using questionable fabrics is just not worth the agony of having HOURS of work wasted on fabric that will not hold up.