Managed to crack the Brush plotting changes today. Basically, the user can hold CTRL when plotting a Brush to mask out Tile 0 - this allows genuine Brush transparency. However, I hit upon the idea of making CTRL mask out the currently selected tile - that way, the user can specify exactly which tile in the Brush they don't wish to plot.
Confused? Ok, imagine the map is filled with Tile 4, and on top of this the user has drawn a shape with Tile 3. Imagine they wanted to plot this brush on to a background consisting of Tile 8 - plotting the brush as-is will cause the instances of Tile 4 to be plotted too.
Using my new system, once the Brush is grabbed the user simply selects Tile 4, then holds CTRL as they plot their Brush - only Tile 3 is plotted, any instances of Tile 4 in the Brush are ignored (it's much easier to understand when you see it working!).
After toiling away for an hour or so, I managed to override the conflicts associated with Masked Tiles, and the whole system was working perfectly. I'm extremely pleased with the Editor's Brush functions, and it's getting to the point where I'm itching to stop coding and start messing around with maps :)
