I have taken years of Japanese. I studied abroad in Japan in a university with virtually no English speakers. The result is that I am more or less fluent, and that at some point I decided to start buying some manga in the original Japanese because it usually comes at a lower cost. Genshiken is an example.
However, by doing so, I am also directly taking away from sales of the Del Rey release in respect to me personally. At the same time, though, my early fandom into Genshiken I know has caused other people to pick up the manga as it was being released her. My consistent and long-term Ogiue fandom has caused people to take notice of Genshiken, buy it, read it, and enjoy it immensely. If I had never started reading the Japanese versions, this may not have happened. So it’s tricky to say, at least as it concerns myself and my interactions with others, whether or not this has hurt the chances of certain things succeeding in the US.
I think there may be a certain balance, and that there is a potential point where if too many anime fans were fluent in Japanese, it would hurt the domestic industry, but that with a certain percentage of fans as Japanese-literate that it may actually be very beneficial. This might sound like I’m encouraging a portion of the anime-viewing population to remain ignorant, but that’s not the case, and the chances of “too much” of the population learning Japanese leans on the slim side anyway.