well fan service isn't really much of a thing that draws me to a manga so w.e, but to stay on topic i suppose negi getting a fever and waking up to seeing chacha bathing was a pretty good scene.
AS for shizuna, ken made several characters based on real live people he knows, like that chigusa girl in kyoto ark, and that guy keechi guy in the tournament arc.
Basically all the people he made based on his co-workers and real ppl, play small parts, and end up gone. Shizuna if i remember, was based on his wife....
Shes just a minor char and i doubt will play any further into this, and no it was never shown that she knew about magic.
as for to love ru, well i read his earlier work called black cat, since im sort of a fan ,i didn't want to see the little girl as part of some harem, in another manga.That's about the only reason i don't read it.