Wow. This has been painful to read. I just upgraded, T2i to 7D, not the same ballpark, I know, but it was a worthy move. The 7D makes up for everything the T2i lacked, but still feels homey and familiar. I can imagine that a move from a 5Dc to a 5D2 would be quite similar, but you would end up gaining way, way more then you would be leaving behind.
The 5D original garnered the "classic" title for being the first of its kind and having a very film-like quality to its images, but the real classic will be the 5D2. Look at how many movies and television shows have been shot with it. And the images it produces are so different than anything that came before it, and it still stands apart from everything that has come after it. Its different. You know 5D2 images when you see them. They have a quality that other cameras don't. I don't know what it is, I just know it when I see it.
Now take all that, add a focusing system that appears to be dead on and takes the image a step beyond the mark 2's haze into a realm of crystal clarity, add a few more fps and some ridiculous leaps and bounds in ISO, and you have the 5D3. I cannot wait to see feature films that have been shot with this camera. I can't wait to see how far some of you folks push this body in the imaging field.
What it boils down to though OP, is what you want. All we can do is offer opinions. Go rent one of the newer bodies. See if it improves your shots like you imagine it would. If it does, buy it. If not, you have a great camera--shoot it 'til the shutter falls off.