By JENNIFER FORKER, For The Associated Press DENVER — As the saying goes, everything old is new again, and sometimes that includes modern furniture. The appeal of modern design’s spare lines and forms has combined with the desire to reduce, reuse and recycle, and the result is high-end, streamlined furniture and accessories for the home. These often pricey items can’t simply look good; they have to perform well, too. ‘‘It’s got to have all the qualities of any other kind of furniture or accessory you would normally buy,’’ says Jill Warner, owner of Mod Livin’, which sells modern and retro furniture in Denver. While going green appeals to many buyers, most people ‘‘don’t want to spend more money because it’s green,’’ says Warner. She maintains that design, pure and simple, drives a buyer’s decision-making. ‘‘As long as the design is modern and attractive, it will sell,’’ she says of the furniture, some made from recycled materials, in her 10,000-square-foot store.