Hmm, you're right, I need better sources - *googles, since apparently that's what the 2chan guy did to get all this info*
It seems true that Gosho really did give a lecture at his former university (Nihon University College of Art), according to the university's website. This page talks about the Nichigei Award for Excellence, which Gosho apparently received this year - the website mentions that the award ceremony was moved from March 11th to April 8th due to the 2011 Tohoku earthquake and tsunami, so the ceremony happened this year. This website also mentions that the university plans on having the two winners (one of whom is Gosho) give a lecture later. (授賞式は、3月11日の東日本大震災から間もない4月8日、芸術学部新入生歓迎式プログラムとして江古田キャンパスの大ホールで行われ、ご出席いただいた林真理子氏からは、壇上から受賞の喜びとともに励ましの言葉が述べられました。また、仕事の都合で残念ながら欠席された青山剛昌氏は、ビデオで心あたたまるメッセージを届けてくださいました。お二人には後日、学内で講演を行っていただく予定です。)
Then this fan website says that the lecture commemorating the Nichigei Award for Excellence is held on June 24th 2011 from 2pm at Nihon University College of Art Ekoda Hall. Apparently only university students could attend. (学部所属の学生さんのみ参加可能 ... 2011/06/24の14時から、日本大学芸術学部の江古田大ホールで日藝賞記念講演会として、青山先生の講演が行われます。)
One more evidence for the lecture! The university's blog mentions that Gosho's lecture is on June 24th 2011. Here's the poster from that blog:
Okay, the fact that the lecture happened on June 24th 2011 at Gosho's alma mater seems legit . . . BRB googling more.
EDIT: Also, you have to admit that, while 2chan may not be 100% accurate, they do turn out to be mostly right most of the times. ^^; I mean, I learned about OtonaFami from there, and I always go to the 2chan Shonen Sunday Spoilers board to check for the latest spoilers on the latest Conan file, which has turned out to be pretty accurate so far. I'm also impressed that the lecture turned out to be true, as well.
EDIT2: Found one evidence for claim that "Gosho said Agasa isn't BO boss" via Twitter! This 青木敬士 (Aoki Keishi) person is, according to his profile, the Associate Professor at Nihon University of Art, Literary Arts(Creative Writing), and apparently organized the lecture that Gosho gave on June 24th (this tweet says that, since he is organizing the lecture, his classes are cancelled for those days). He also lent his pen to Aoyama when Aoyama was signing signatures, and he got excited and jokingly tweeted that maybe he should take care not to wipe off Gosho's fingerprints (lol).
Oh! I found Nihon University's profile on Aoki Keishi.