This post was inspired by Aimée's post Reduce, Reuse, Recycle. I have used examples from her post for the sake of convenience. Feel free to substitute names of journals and conferences in your field as you read.
I've written on my own blog about the tensions between publishing for validation and publishing for communication. While you will be judged (and validated as a scholar) based on your publications, the primary reason for publishing and presenting your work at conferences, public lectures, or wherever, should be to communicate.
If you have a communication orientation to your work, the recycling issue appears in a very different light.
Audience makes a difference
The list of occasions on which Aimée had presented similar work looked to me like it spanned a range of different audiences:
I've been joking that what I've been creating this week, in preparation, is a "Frankenpaper": parts of Saturday's 15 minute conference paper is built from text I created for a public talk in the Digital Media Series at Stratford, reworked for a lecture celebrating 50 years of the Faculty of Arts at UW, and then reframed in a minor way for an invited lecture hosted by the MA in Humanities at Laurentian University in Sudbury. Incidentally, those talks all revisited ideas and prose I first considered and wrote in 2005, for the Reader's Forum of English Studies in Canada. Still with me? Okay. My conference paper is also built from an article I've recently submitted to Biography--which was written from the ideas I pulled together for a different conference paper for last summer's International Auto/Biography Association conference in Sussex. Oops, I did pull stuff right from the conference paper, too, that I had removed from the article version of that research. The Keynote slides draw from the Stratford/Arts/Sudbury presentation, as well as from the IABA presentation.
The audiences for those various public talks are unlikely to overlap. Local events, like celebrations of 50 years of the Faculty of Arts, draw a local crowd. Public talks have a different audience from academic conferences. And different academic conferences have different groups of people. The Auto/Biography crowd are not the same as the English Studies crowd. (I know, for example, that there are sociologists in the former.)
The same can be said for different print (or online) publications. The people who read Biography are not the same as the people who read English Studies in Canada. And they certainly aren't the same people who read journals in communication studies, digital media, or whatever.
The fact that you've heard it before doesn't mean everyone in your audience has heard it before.
Audience also affects the content
In addition, each of those presentations/publications will not be exactly the same.
All research communication contributes to ongoing conversations. Those may be formal theoretical conversations happening in peer reviewed academic journals. Or they may be public debates taking place in the mainstream media and people's living rooms. The general public are interested in your research in a different way than the students in an MA in Humanities, or your disciplinary colleagues at an academic conference. And you want to communicate something different to those different audiences, too. You will be engaging with them in different ways.
You will also contextualize your findings (empirical, conceptual, theoretical) in ways that are relevant to a particular audience. A paper for the International Auto/Biography Association will be different from a paper for English Studies in Canada because you have to make different assumptions about the audience's familiarity with particular debates that you engage with, at the very least. A public presentation on Digital Media is more likely to be contextualized in public debates happening in mainstream media than theoretical debates happening in academic journals.
Chances are that you are publishing/presenting to those different audiences because you have contributions to make to different debates and those debates are happening in different places. Although the content overlaps, you have something slightly different to say about your research to those different audiences.
Again, just because you've said this before doesn't mean you have. Or that you've said it in a way that this audience can engage with.
People need to hear what you have to say
Presenting/publishing in multiple venues is not "recycling" so much as giving people multiple opportunities to come across your work. If you only produce one publication/presentation from a given research project, you rely on the people that need to know what you've discovered/created finding that one place where you've told anyone about it.
It's like the proverbial light under the bushel. It's there. And if you know it's there and lift up the bushel basket, you can see the light. But most people aren't going to notice. If you have something worth saying, it's worth saying in venues (live, online, in print) where the people who need to hear it can find it easily. You don't need big gaudy neon signs but you need to be visible.
In doing this remember that any oral presentation is reaching a much smaller potential audience than a written publication. People are there to hear it or not. Whereas a print (including online) publication can be engaged with at another time, even years later. One reason to turn your academic conference papers into academic journal articles is to make them accessible to people that weren't there, including people that won't even be interested in your topic until 2 years from now. And if you want to reach people who don't read academic journals, you need to also publish your work in venues they frequent -- blogs, magazines, public talks, etc.
That ability to access the paper asynchronously (to use the fancy online learning jargon) also means that readers/listeners can refer others to your work. Maybe Jane heard your paper at that conference and thought it was really interesting. She knows people who could really use that knowledge. Is there a way for her to tell people about it and get them access to what you presented/published?
Validation is still importantThe processes that validate your work as an academic only recognize some of those publications: the ones that communicate to audiences they value. If you want recognition and validation by peers in your discipline then presenting at conferences in your discipline and publishing in peer reviewed journals in your discipline is important. The fact that you also communicate to peers in cognate disciplines or interdisciplinary fields is likely to enhance your reputation in your field. Those publications will probably not substitute for publications in your discipline.
Communicating to non-academic audiences may also be valued in this additional way, though peers are likely to wonder what the time you spend on that is taking away from things they value more.
The question is, why are you writing/presenting? Who do you want to reach? What do you value? Organize your publication/presentation strategy accordingly.
In the end, you are probably more at risk of publishing too little than publishing too much. Stop worrying about recycling.