Oh yeah, you can easily bill a month of full-time work for fixing an old app with a busted data model. After that you reach the place where you can sell a change that takes 30 minutes of work for $150 and really do it in 30 minutes, but getting there is expensive...
I'm at the point now where the time invested in the project has paid off - I understand the business problems much better now, and some of the intricate work I did months ago is paying off in spades (basically, having put together a flexible data model up front). Things that might have taken days to do before I can do and redo in minutes or hours. But it's taken way too long to get here, and ultimately this is a one-off - most of the knowledge gained isn't transferable to any other projects directly.
