Thanks a lot, Marco and Metin.
Following your advices I got some 2M polygons on the export
and after importing into 3DCoat the "white spots" had decreased.
Now, 3D Coat crahed several times in the texture painting process, though.
So, no chance to further increasing polygons in Moi.
Thanks a lot for your appreciation regarding little suggestions I gave you.
Unfortunately right now I'm very, very busy at work and I can't provide a decent help.
But I strongly suggest you to start a new topic in 3D-Coat forum and, if you can, to upload there your obj files.
3D-Coat forum provides a great support from Pilgway's developers and from many advanced users.
It's not necessary to upload ultra-high tessellated versions of your objs.
There are too many variables that come into play when it comes to importing for Per-Pixel-Painting in 3D-Coat,
and the experience of advanced users could solve your problem.