I personally find the controll scheme a bit odd...
Dragging with middle click of left click seems way more intuitve than shift clicking, since you could get rid of the need to keep one hand on the keyboard, which you barely need anyways...
At first I tried to drag the sliders left and right, instead of up and down, which is possibly due to my unity background.
A preview window, which shows your texture in a tiled grid would be really helpful in order to see how your texture looks in the final result.
Another cool feature would be the ability to draw on one of the tiles or to add your own image files to edit...
It would also be efficient to be able to replace connections directly, rather than having to remove one and stick the other one on...
Apart from that it's a really good tool... Keep up the good work