Apart from very simple libraries with very limited functionality (the servo library being a good example) I believe it would be more useful to spend time writing a tutorial from which Arduino people could learn how to do something rather than spending the same amount of time writing some code to save them the trouble of learning it.
With a tutorial you would be sharing your knowledge with the Arduino community and less experienced people would learn stuff, and probably learn incidental skills and techniques with wider application.
Complex libraries usually (always?) go wrong (or don't exactly meet the user's need) so that the user just wastes time trying to understand and fix the library which would be better spent on their own project.
Of course I might be tempted to soften my views if you intend to include extensive documentation with your library - the sort one would expect to find with a commercial product.
Just my 3 cents worth.
...R