Software is not an asset - I know everyone thinks it is, but its not; its a liability - its very existence generates cost. Every minute someone spends coping with it in order to adjust the behavior of hardware (which is an asset) is a net-credit on the balance sheet and a decrease in profitability. A necessary expense in many cases, but a cost nonetheless. Getting rid of it goes directly to the bottom line.
Software isn't a thing - its a form of communication. Just as no one would list meeting minutes, or recordings of the CEO's speech as company assets, software should be seen as stored communications (with hardware). Its value should be viewed in how it changes behavior; its very existence should be seen as creating risk, and its deletion as key to a healthy techno-ecosystem.
This is the essential argument behind why refactoring is worthwhile, and why its value isn't really comparable to writing code. Its also why its hard for non-programmers to see that value - because they think of programmer time as a credit, when really its can also be a debit.
My advice to managers (and everyone else): Want a sure fire way to add value to your organization? Reward and encourage deleting of unused code; fight for and insist that programmers be given time to refactor and otherwise eliminate unused code, and don't account for time spent doing so in the same way you do the creation of code.
My advice to programmers: Delete unused code at every opportunity and scale (function, class, file, project, organization); don't compare the effort to do so to writing code; work at all times to have your software feature-set reflect its actual, operational use.