I've dealt with both: 1. maintenance coding 2. re-write coding
Re-writes take forever, because a lot of the edge cases and bug fixes are lost [1]. You might think they go away, and some do, but new ones are introduced. QA process is critical. Management becomes critical of excuses, and the longer the project is drawn out, the more they get involved. The final shift to a new system is never one-and-done. Management is paying for two systems, canary deploy.
Smaller re-writes are the ideal practice, and your code base is set up this way already, right?
Re-writes take forever, because a lot of the edge cases and bug fixes are lost [1]. You might think they go away, and some do, but new ones are introduced. QA process is critical. Management becomes critical of excuses, and the longer the project is drawn out, the more they get involved. The final shift to a new system is never one-and-done. Management is paying for two systems, canary deploy.
Smaller re-writes are the ideal practice, and your code base is set up this way already, right?
Maintenance code is cheapest.
[1] https://www.joelonsoftware.com/2000/04/06/things-you-should-...