If you don't use the same settings as the tilemap object, you'll have the same problems - the sprites will seam along the edges. And it will be slower, because the tilemap object has unique optimisations. So why not just use the tilemap object?
Hi Ashley, with the sprites i can make them 1 or 2 pixels bigger, and i don't have the seams problem anymore.
<img src="https://dl.dropboxusercontent.com/u/46383802/report/tiles1.png" border="0" />
About the performance, i only use the Auto tile sprites in the edges of the "terrains", and those sprites will be only a fraction of the total graphic assets, and i aim mainly for PC games with much better performance than mobile.
<img src="https://dl.dropboxusercontent.com/u/46383802/report/tiles2.png" border="0" />
Take a look at a structure like this, even with the Tile map object it would take a few minutes to figure out how to assemble the correct graphic tiles, and if you draw the sprites directly and use the auto tile function, it would take just a few seconds.
<img src="https://dl.dropboxusercontent.com/u/46383802/report/tiles3.png" border="0" />
But don't worry, it seems like i am the only one who would take advantage of this...