I think it would be a good idea to use the brushes for a texture map in the transparancy of the shader of the tabard. Then you can use them to 'eat away' the cloth. And you can use them in the texture part of the shader, to add dirt and grime. On the render you could use them with the 'smear' tool, to 'push' colored pixels in or out the cloth. The color will always be right then, but you will distort the background too. If you use them with the clone tool, you can clone parts of the background on the clothin, to make it look like it is not there. Another way of using them, is to make a second render without the character, place that version behind the main render, and add a mask to the top layer. When you paint with the brushes (in black), the layer below will be revealed, which looks like the tabart is frayed. Just using them with plain color is hard to do.