Just had another idea. Similar to the preview in Phoebus' tileset assembler, it would be very useful to have some "composite screenshot" window in Raw Explorer.
That is, a mockup screenshot of DF where you have a 16x16 area or whatever and you can set each tile to contain what you want. So for example you set it to display grass tiles, place some trees and walls, some creatures, etc.
It would be very useful to fine tune colors for contrast and visibility, look at creature graphics in a "natural environment" and how they stick out, see how various tiles work together and so on.