Canon 5D classic. Should I buy?

[MyFirstCam]

Im looking at a 5D with sigma 28-70 2.8f lens for about 1500 USD. all second hand of course.

Is i worth it? should I buy more lenses for my Nikon D3000 with lens kit. insteead with the risk of having to sell it all again when I want a new cam?

Seems like the 5D is a really good cam (better colors, details with fullframe, sharpness and so on...). It would definitely take care of all the problems I have with noise, lack of functions and so on because my cam is cheap.

I am still somewhat new to photo, but i really want to keep on.

So many questions in my mind right now.

Any help???