" With regards to collada, there could possibly be some bugs. Would you be able to post one of the collada files that appear broken?"
I will as soon as I get home I'll post the same OBJ and collada
"If you just need the same UV set in each layer, it seems like you can rely on these defaults and use objs."
The problem is that in my workflow I import a file with different shading group assigned per material (stone_SG, metal_SG, Wood_SG, RoofTiles_SG), I then comp split it by material name in CE and assign a random Texture to the new shapes according to the material using the UVs it has.
The problem is that for this to work the color.map needs to be tiled several times (TileUV (0,2,2) for instance,) but the dirtmap ( a leak texture) doesn't need this treatment.
Once I use theTileUV (0,2,2) operation though, this tiling get copied into the dirtmap and the dirtmap gets tiled too which is not good.