Maintenance Debt

I manage a group of engineers at a startup and am gearing up to start a "sustainability" push. That is I'm looking at ways to get our codebase on a more sustainable footing -- perhaps more on that later. It occurred to me that the notion of a "maintenance debt" is worth some thought. What I mean by "maintenance debt" is that maintenance, documentation, refactoring, and code quality can be deferred. As you defer it you accumulate a debt of maintenance that may need to be paid back. Obviously, this happens in other circumstances too -- my experience as president of a HOA being a painful illustration. But I think startups may be a special case.
When you start a software company you typically are under-resourced, must ship a product quickly and have little certainty about either the long-term fate of the company or its initial product. In this case, does it make sense to invest your limited resources in order to keep your maintenance debt low? Likely not.

Maintenance debt it is like "real" debt in several ways. First, "interest" must be paid, that is the longer you defer paying down the debt the larger the debt to be paid down. Second, it provides leverage on your investment dollars in exactly the same way that "real" debt does.
But maintenance debt is unlike "real" debt in other important ways. First, it doesn't appear on your balance sheet. This can be both good and bad. It's good from a financials perspective, but bad in the sense that your Board may not appreciate the value in paying it off. Second, you may get away without paying it off. That is should your project or endeavor not succeed you don't have to pay off the debt (much like a bankruptcy). Third, there can be non-linear effects on maintenance debt. For example, the departure of a key team member may greatly increase the debt burden.

The questions for me now are: is it time to start paying off the debt? what is the best way to do this? how much of it can be side-stepped?
I've been thinking about ways to avoid paying some of this debt and may write more on this later.

The other important issue is how do we think about managing maintenance debt more explicitly in the future.

Update:
I was just pointed to this related post.
http://www.codinghorror.com/blog/2009/02/paying-down-your-technical-debt.html