Keep pace with the Technology: The way technologies are changing at a very fast pace, it will be foolish to stay with your legacy technology running for years whereas the world is adopting newer technologies for the similar kind of projects. There is no doubt that when the existing technology was selected, it would have been a state of the art and latest of the technologies kind of solution. But remember that over a period of time, technologies get faded away in wake of newer, robust and advanced technology entrants.
Remember that development for all business apps start with a prerequisite set of requirements basis which timelines and plans are built and team sizing, resources etc. are set. Once this business requirement is converted to an app, it is released on Test Server, Staging Server and Live Server respectively for QC, UAT and go-live in the same pattern. Gradually when this app is handed over to end users on go-live environment, the app usage starts triggering along with the desired business results chickening out.
But story does not end here. New requirements that either go to changes in existing functionalities or new functionality built keep pouring in there by reshaping the size and environment of your existing app. That is where your awareness towards newer technologies to manage and control any kind of crunch in the existing one, is very critical.