I'm always happy to say it: maintenance people are the ones who keep the world turning. This isn't worth noting because their job is fundamentally harder than other jobs. It's not because they do something that others cannot. It's because theirs is a craft of delivering, and delivering now. In addition to having the skills to take another person's work (or errors) and make them sing again, these men and women need to respond instantly and be at the top of their game until the job is done.
It's easy to find reasons that working on legacy designs and installations isn't fun. It's old technology, solutions are bound by design decisions others have made, and it can be frustrating to spend nights and weekends on another engineer's problems. The job can also be thankless at times, such as recreating documentation so future engineers won't waste their time on bad information. And because designs are rarely retired, it can be difficult to gain a sense of long-term accomplishment. In the back of your mind you know that the design isn't perfect and will need attention sooner or later if it is to remain in production.
However I think that for the right person the aforementioned negatives are more than overcome by the opportunity for a job that is dynamic, fast paced, and very rewarding. The chance for a maintenance person to become a company's all star occurs at least a few times a year, and there's nothing more fun than doing a great job and getting the corresponding recognition.
Near the beginning of my career, I worked at Keithley Instruments in Cleveland on the Manufacturing Design Engineering team. While the job was unique in the number and variety of tasks that the position required, there was one thing that got me noticed in the organization: maintaining legacy products. I was responsible for making sure we could continue to ship products to our customers, and I would be the first one called when a slew of units couldn't pass quality testing. Everyone notices when something suddenly stops working, especially if the interruption of service results in an interruption of revenue. When a Keithley line went down, I was in a position to jump in and work on the solution while everyone was watching, hoping, and cheering. Once a solution was found, there was an infinite source of kudos for everyone involved: engineers, technicians, purchasing, manufacturing, line workers, etc...
So the next time you're working hard on a maintenance or legacy task that seems silly, frustrating, or drab, remember that it's not all bad. You never know if someone is watching you create great work, and even if they aren't the might watch your next job, or the next. Soon enough you will be there to save the day!