NaNoWriMo isn't a reasonable goal for everyone (and not for me either), but it's a meaningful badge of honour. I think there are other events with a similar recipe but an investment that would suit you better (some LJ communities, blog festivals, etc).
Tossing out work would be counter-productive, but I think rewriting your material from an outline would be within the letter and spirit of the rules. Boxing the project into a fixed time period (aside from any preparatory work) is good for motivation: you won't throw good time after bad in a project that is getting stale (when working knowledge and motivation have dwindled), you'll just reuse the same abilities you were cultivating the first time but with a bit more ease; you'll be communing with a large group of people sharing your joys and trials and egging you on.
Tossing out work would be counter-productive, but I think rewriting your material from an outline would be within the letter and spirit of the rules. Boxing the project into a fixed time period (aside from any preparatory work) is good for motivation: you won't throw good time after bad in a project that is getting stale (when working knowledge and motivation have dwindled), you'll just reuse the same abilities you were cultivating the first time but with a bit more ease; you'll be communing with a large group of people sharing your joys and trials and egging you on.