I'm tempted to skip plain greys and go with one warm and one cool grey ramp. When you draw with markers, it looks good if you use different temperatures.
Looking at my histogram, grey gets a huge amount of hits, but with games / art it's more useful to explore the more saturated regions of space. Still, I could probably convert a few of my more grayish colors and the plain grey ramp into two warm and cool ramps.
On the other hand... my plain greys can be made to look cool and warm when placed adjacent to other colors, and as neutral grays they bridge better to any given color. But with cool and warm ramps I could also bridge, with more fitting hues to choose from. I guess someone who has used the C64 palette is more suitable than me to be a judge on this matter.
I should probably take a look at the Chaos Engine and Speedball palettes. They have a lot of nice hues in the greys, iirc.