There's an idea. You could take the "copy from existing page" code and automate that to copy modules to many pages at once.

DNN does not have currently have this ability in the Admin UI.

If you create a module that allows you to copy a specific module instance to many pages at once and make it available to the community that would be a nice extension.

I have always thought it would be nice to mark a module as "Display on these Pages" with a list of pages you can check off.  Instead of "Display on all pages" which inevitably causes problems.

I don't know of anything like this that is already available.

Well, developer I may be, but customizing the admin interface is still a bit beyond my capabilities with DNN right now!  The best I'll be able to do is do the updates directly, or build my own external, simplified interface for this functionality.  But I agree, an extension along these lines would be great.