Out of curiosity here, what sort of limit would you suggest be put on the number of tiles displayed on the screen at a time? I was prototyping something in SGDK2 where I wanted very small tiles and lots of them on the screen at a time, and it caused the system to slow down considerably. To make sure it wasn't just my calculations that were slowing the system down, I removed all of the calculations, and the system was still running rather slowly (~25 FPS). So the question is: what would you put as a minimum on tile size?
Also, while working on this, I found that pressing the delete key anywhere in the Tileset editor assumes you want to delete a tile, but if focus is in the Tile Size textboxes, it should instead delete the text.