Very interesting findings, but I am bit confused with my initial testings. I found the default settings very conservative, at least compared with my other compact camera(Canon A570 is).
My initial settings are Contrast+1, Colour+1. Sharp 0 for landscape
For portraits I am using Contrast 0, Colour-1, Sharp -1
B/W: Contrast+2, Sharp +1
In general I will try to get a good JPG settings to avoid post processing