Seems to me that a combination of the two would be pretty great. For eroges, I think that something like systran, but with an extremely large dictionary of common words, phrasings etc*. might be acceptable for playing fairly simple games. I don’t know anything about systran; how much it costs, or if it even lets you create a dictionary etc. but that might just be the way to go.
Of course, it’ll break apart on trying to play anything slightly more complex than Triangle Heart, so the best solution would really be to go learn Japanese after all!
*specifically targeted towards eroges, too, because they have their own writing style compared to books and webpages, with a fairly large set of common phrasings
