@Ben the new dynamic grid is great (as implemented in 184.108.40.2061), but still not ideal.
I'm working on an icon collection. I had setup a custom advanced grid (which is still not dynamic) with 64x64 pixel tiles for the icons that have a slim 16 pixel gutter horizontally just for visual separation and a bigger 32 pixel gutter vertically to have space for a icon name label. Within the 64x64 tiles my only option is the number of divisions. I chose 16. Symmetry and centering is a big thing in icons, so having instead the dynamic subdivision based on zoom would be much better. With maybe two parameters, 1) number of divisions per zoom level, 2) number of zoom levels visible (currently only two, up to three of four would be nice, getting progressively faint). That way I can get clear lines at the center of each icon, level two at quarters and level three at eights. And it all jumps by a factor of 0.5 when I zoom in more.