Is it possible to publish too much in one (somewhat specialized) journal?
No and yes.
No: Does it really matter? As long as the journal has effective standards of some sort, is respected in its field, and is part of the Science Citation Index, why not publish a lot in one journal? Your papers will be read if anyone is interested whether you publish exclusively in the Journal of Pink Kangaroo Studies (JPKS) vs. half in JPKS and half in the JMKS (Journal of Mauve Kangaroo Studies).
Yes: If you publish exclusively in one journal that is quite specialized, your research may appear narrow, and these days, narrow is not highly admired. Furthermore, people might wonder: Do you have some special deal going with the editor? Does this journal publish anything you send them no matter what? Is the editor a close friend or relative, or are you so well known that the editor assumes that all your papers are great even if they aren’t? One of my favorite journals is in danger of becoming the Journal of One Famous Obnoxious* Person, and I don’t think that’s a good thing.
If you have the option of publishing in a range of respected journals, I think it is good to publish in many/all of them, but it is fine if there's one (or two) that you publish in much more often than in others, but perhaps I only think that because that is what I do.
* Please disregard this adjective; it is irrelevant to the point.
10 years ago