The developers building new applications are very nice people, of course. But the real heroes of the programming world are the developers maintaining and extending existing applications.
Maintaining legacy is equally responsible job like building something from scratch.
It requires good analytical skills to understand someone else piece of code. I think no developer should miss an opportunity when asked to maintain or support long running project as it will help developer to learn by looking at the application which is not build by him/her. Long running project are good example of their strong architecture and developer should be proud to be part of legacy projects.
At the same time, maintenance projects gives developers an opportunity to apply latest technologies and practices which they have learned in their past projects.
I Found this interesting article on visualstudiomagazine.com for more detail click