For projects in maintenance mode, think about what comes next. What will eventually make them unattractive to your customers? To avoid obsolescence, do they need new features, better performance, or to be simplified? If you start over, can some projects be merged? Should they be built with different tools, languages, or processes? Are there improvements or directions that no one's considered? Have your developers answer some of these questions. Build prototypes. Try a new language or framework. Give a project a new mobile interface.
ItIt's easier to experiment with alternatives when there's no looming deadline. Use the dull times to out-maneuver your competitors.