I don't think your reasoning quite stacks up.  There's probably a huge market for this type of stuff in Japan, which would explain how large the hentai industry over there is.  If it's hard to profit, then there won't be many of it.
As for the English translation, it's probably difficult to get it in stores, so maybe it'll mostly be download.  Sales wise, it may be difficult to judge at this point, but if there's any correlation with the Japanese market, it could work.
Young adults may not make the most money, but they generally don't have many costs, which kinda balances things out.  Especially if you're working.
Generally, these types of things are fairly price inelastic (like drugs) so you can make a fair bit of profit per sale.

(This post was last modified: 30/09/2010 08:55 PM by ZiNgA BuRgA.)