As the Internet prevails, I came across article and even the built-in camera help indicating that the Adobe RGB has a wider gamut, hinting its bigger advantage over the conventional sRGB palette. But whenever I use it, I tend to get duller images which tend to contradict my assumption.
In short, the theoretical gain in using Adobe RGB can only be derived with the appropriate software like Aperture 2.x. and more post processing. Otherwise, you are better off sticking with sRGB to shoot most images. Its not worth the trouble for amateur like me.