A glut of hand-me-downs from downsizing baby boomers has caused the value of many heirlooms to drop in the past 20 years. Below are a few examples provided by antiques expert Terry Kovel, newspaper columnist and author of the annual Kovels’ Antiques & Collectibles Price Guide. • Royal Doulton balloon man figurine. Was $150 to $225. Now $30. • Fenton milk glass candleholder. Was $47.50. Now $35. • Arts and Crafts dining set. Eight-chair set was $9,400. Now, four-chair set $1,0