I feel envious of your prime lens collection! I think for most situations I'd be much happier with a single mid-range zoom. In fact, the only prime I own is the lowly 50mm f/1.8). But if you have the patience to manage multiple lenses, and change them when the situation calls for it, you'll certainly get the (technically) best images. Sounds like you've got it figured out pretty well though.
I guess my original point, though, was that the original posted wanted a walkabout lens, and I'd further argue that the vast majority of photographs, when walking about, would prefer a single versatile zoom, even at the expense of sharpness. If you're a casual photography, and you miss the shot of your kid blowing bubbles/laughing/running because you're busy changing from one lens to another, then it doesn't really matter how sharp the prime "would have been".
Anyway, good feedback.
Take Care,
Eric
Your points are valid. However, if you look at the 24-105mm zoom, sometimes your legs might be able to do that zoom for you. Walk about lens has many definition, some people uses the 50mm, the 35mm, the 85mm and etc. So it depends. Just hope TS will make informed decision for his purchased.