I want to buy a FF Canon Camera, I´m not a profesional, but I would like to have a good camera. Do you think it is good idea to buy Canon 6D or wait for Canon 6D mark ii??
Rent the 6D.
Do your night shooting with the 500D and the 6D. Compare the results.
This will give you an idea if the 6D is what you are looking for.
A hypothetical 6D2 doesn't take any pictures right now. It will probably take better pictures than the 6D1 though, but so will the 6D3, 6D4 and 6D12.
Only a direct comparison will tell you if buying a 6D is justifiable. It will provide pointers towards if it makes sense (to you!) if waiting for a 6D2 is justifiable.
There were rumors last year about a hypothetical 6DmkII due to the 6D being labelled as discontinued -- which turns out was not so true. Nothing confirmed AFAIK.
What I would do is try to defer the decision until when you feel you absolutely need a new camera (old one dies out, imminent trip/wedding/shooting opportunity requiring a better body, etc.) Not that the 6D is a bad camera, but there's nothing as frustrating as buying gear only to find out weeks after that it was the end of a cycle and a new version comes out ;) At least, I know that's how I would feel.