From what you know, i think the first statement is a bit generalised, and shouldn't be said for any old palette, but for a single ramp. With the second, i would say that any colours that do not 'add' to the piece, aren't needed, or ones which are not noticable in the required res. Smaller doesn't always mean better, but palettes with really refined and useful colours will usually require less of them, than ones with quickly picked and not-thought-through colours.

 

I'm kinda rambling now.

 

With the last two, i would change 'darker colours' to perhaps colours with less light hitting them in the image... if that makes sense. And rather than tinted yellow or blue, the hue leaning more towards the yellow or purple ends of the spectrum. Or something..

 

Lol, hope that helped.