[brownegg]

Congrats on your success--you have the best kind of problem.

1. You have a working product--do not do a full rewrite. Rewriting has so many pitfalls in the best of cases, and if it's just you, the context switches between the "old" (which you will still be spending most of your time maintaining) and the "new" systems will be brutal.

2. This is the prototypical "real world" case. You're basically asking how you can prioritize immediate enhancements vs. long-term flexibility and maintainability. But maintainability is a feature. Any (good) book on agile development methodologies will tell you that consistent refactoring and cleaning of the code has direct user benefit, in that future velocity (user enhancements) will be better.

3. The prudent way forward is to chip away at the problems. As you "touch" various parts of the system, start doing small refactoring work, adding comments, tests, etc. Remember, you're starting from nothing--anything you do in this regard is improving your situation.

4. If you're not doing some sort of iterative development methodology, start. Personally, I have a preference for Scrum, because of its time-boxed nature. It lends itself well to devoting a section of each dev cycle (sprint) to the kind of cleanup work you need to do.

Good luck!