I believe the two of you are looking at the engineering/maintenance problem from different perspectives. From a managerial perspective, the two are the same. You can trade one for the other, with money spent, and you do your calculations. From a technical perspective, they are quite different. Maintenance only repeats the same thing, restoring it to when it was new, but does not change it to something better. Re-engineering it would improve it so it is better than what it was when it was new.