I save both the ply and obj files from ItSeez3D. I take a bust for example and import it into meshmixer. The color texture is trashed for some reason, but with meshmixer, set the print size to whatever you desire (102 mm for a 4" bust for example). Then hollow it out using the 3D print utility to a 4mm shell thickness. Then save the resulting file (.stl).
I'll admit to a lot of confusion with meshmixer size parameters but that's a whole other issue. If you set the size to 102 in meshmixer, then blender thinks it is 102 METERS, so you have to scale it again in blender. Crazy stuff.
I use blender to bake the vertex colors of the original ply and texture file to meshmixer's stl file after aligning them as closely as possible. (you can eyball it, or use meshlab). It can be done and it comes out well. From blender, you can save a vrml file (.wrl) and zip it with the texture.png file that you create and send to printing service like shapeways.
Hope this helps.