I don’t think comparative advantage will keep (inclined) top economists away from blogging:
1. Very good economists can better use blogs to attract an amazing audience; even Dani is seeing the light, and yes his new post does mean that for trade policy he can worry less about low-cost outsourcing! Opportunity cost may be higher but value-created is higher as well for the better economists.
2. A blog can be a loss leader; Greg’s blog promotes his textbook and Dani’s blog helps his new book. Prominent economists are more likely to have promotable ancillary products. Don’t the high productivity companies often spend the most on advertising?
3. Temporary blogging will become more popular. When Ed Glaeser writes for The New York Sun, he is writing for the blogosphere more than he is writing for Sun readers but at the end of the day he doesn’t have to come up with another post for tomorrow.
4. I predict there will arise a rotating blog, run by a consortium of top economists. Figures such as Justin Wolfers will blog their research for two or three weeks and then turn the reigns over to a buddy, moving on, and returning perhaps a year later for another brief stint.
5. If you are wondering about me, I face an especially low marginal cost of blogging and thus I am likely to continue for a long time. For both consumption and research reasons, I was already reading and absorbing lots of outside material (a key base for my blogging content, though I miss being able to read quite as much as I used to), so turning it into blog posts is relatively cheap. Dani and others will probably agree that coming up with the content is the problem, not the actual writing of the post.
Here is another good post on the benefits of econ blogging, stressing the concept of self-experimentation.