Help please: 75/1.8 instead of 35-100?

IMO, that's so easy question considering you already have 25mm F1.4, 45mm F1.8 and 40-150mm zoom. I also have these, as well as 75mm and I never felt a need for 35-100mm.

With these 3 lenses you already cover what 35-100mm would offer, except fast long option. 35-100mm isn't very good in 75-100mm range wide open, Olympus 75mm F1.8 would in fact be a better 75-100mm "zoom" when you crop.
Nothing can replace F1.8 aperture at 75mm in m4/3, especially given beautiful bokeh that Olympus 75mm gives. F2.8 is too slow, even at 100mm. I very rarely use 75mm at F2.8, it shines at F1.8 and F2.0. There is huge difference between F1.8/F2.0 and F2.8.

Zoom only offers you flexibility but you have to give up a lot. Then there is a price. For $600 difference between 75mm and 35-100 you can pick up a second body, like E-PL5, if you don't have one, and mount 45mm on it with 75mm on your main body. This will give you flexibility close to 35-100mm lens and way better IQ.

IMO F2.8 aperture is too slow for m4/3 anyway, F2.8 limits what you can do to what cheap telephoto zooms do in larger sensor cameras.

This is a very good post about 75 vs 35-100, see number of likes. (search works fine in this forum, BTW, that's how I found it):
http://forums.dpreview.com/forums/post/50400952

75 vs 35-100 dilemma is basically a dilemma of quantity vs quality. Flexible zoom will allow you to take a large bunch of good enough photos that you can probably sell. 75mm prime will result fewer number of photos but they can be outstanding.