The marketing-recycling phenomenon began in Minnesota in the Eighties with Once Upon a Child, the notion that kids outgrow their clothes, toys, and furniture so fast it's nuts to just keep buying new, then spread to sports (Play It Again), and lately to the electronic-communications frontier with places like Computer Renaissance. Out in Kendall Irv Richter has been doing bang-up volume on Wilson outfielders' gloves and Rawlings catchers' mitts ($7, $12, $30, depending on condition); exercise benches that go for hundreds at new retail but which he can move for $30; treadmills retailing at Sports Authority for $1800 to $2400 pricing out at $250; and home gyms that sell for $1500 to $3000 new going for between $200 and $600. "The average kid plays different sports in different stages," Richter explains, "and if you're a young mom or dad you might be buying for yourself too." If you can buy good merchandise at half or two-thirds off, what's the point of being snobby about "brand-new" status? Play It Again Sports will even let you give yourself discounts on trade-ins or tradeups, or selling on consignment. Even when the economy rights itself and bin Laden is just a memory, you may never want to return to Bal Harbour to shop again.