How easy is it to adopt an Agile approach when your project involves changes to legacy systems?

My philosophy is that project stakeholders should be involved with modeling and documenting their requirements,  not only do they provide information but they actively do the work as well. 

To make it easier for project stakeholders to be actively involved with requirements modeling and documentation, to reduce the barriers to entry in business parlance.

Software engineering is a competitive market. Every day, a new disruptive service shows up that tries to improve something that somebody else already does well. This creates a very harsh environment for the development of software products; products need to constantly change and evolve in order to avoid losing market advantage to new competitors. But there comes the biggest issue with legacy software - it is extremely hard to change.

Legacy software engineers spend months, even years, adding more and more features to the product by simply injecting new logic until the point where injecting new logic becomes so risky and difficult that adding even the simplest of features might take weeks.

If the risk and complexities associated with change continue to grow, eventually the cost of adding a new feature will greatly outweigh its value. In time, the project simply becomes unsustainable and the business will start to lose market advantage to new players and face a slow and painful death