This is a question about assessing the cost/benefit or ROI of a prospective project.
I'm working in 6-8 old years software project. It has a lot of issues and also failures plus some failed people on its way. Right now after raising the project (software application) from the dead, when the new requirement comes, the developers are looking in the code (not in the working features in terms of usage) the corresponding code. There are ideas of creating, rewriting the project from the beginning. I wonder if there is a sense from your point of view to look in the old code something that corresponds the new requirement for the current application? Because if it is different, then the developers are getting back to the requester, describing what they found in the code, and once again discuss requirement.
In one side it fosters requirements engineering and requirements gathering process, on the other hand it may be waste or unnecessary extension of the time. Because it may be better and faster start from scratch with the new code for the new feature. And especially if the new system or rewriting the system can be the case.
While there may be opinions on this subject, it would be helpful to find a methodology so I could recommend whether the stakeholders are better off continuing to invest in the old code or build from scratch?