Three and a half years after I asked this question and I have to say (in my case) that NOT talking about an anime did nothing towards stopping others from collecting from them because:
1. I mostly like niche anime that less people are into so talking about them doesn't make any difference even if they were all commercially released in English.
2. Because of #1, 80 percent of the people I bid against are Japanese collectors and they would never be the slightest affected by what I say.
3. I've learned since then how very few non-Japanese fluent people want to watch raw anime. They don't have an incentive to do so since they wouldn't understand (that) much of what they are saying. I took a very "me" centered point-of-view when I asked that question.
On the other hand, some people have mentioned in other threads recently that they hold off posting a few things so as to not encourage someone from starting to collect from it (or at least to discourage raising the prices a bit from what they would have gone for otherwise).
What has been your experience on the "not-posting items" issue?