Ahh, half assed sequel titles, well what else to expect here?
However, it is no worse than the terribad sequel titles that plague hollywood that contain overused words like "resurrection" "reloaded", or my favorite-- xtreme/extreme, etc in an attempt to sound badass. Then again, "Ore no Imouto ga Konnani Kawaii Wake ga Nai Xtreme" would sound like the kind of anime that wouldn't be appropriate for these forums.
Personally, I wouldn't mind just calling it II, but hey!