Honestly, unless you are shooting professionally and have high demanding clients or unless you absolutely must make your gear as light as possible, don't worry about a carbon fiber tripod.
I have one, only because I had to make my gear as light as possible since it's for taking on holiday with me. But I'm no pro. Before my carbon fiber tripod I had a cheap aluminum one that cost about £60. And as long as I wasn't shooting in demanding conditions, such as bad weather, the pictures came out no better than with my newer tripod.
As for the weight differences, you'd have to look up whatever model of tripod you were interested in. As a rough guide though, My carbon fiber tripod legs weigh about 1kg and I think the aluminum version was about 1.5kg. Doesn't sound a lot but also depends on how much you will have to carry it.
Just forgot to add, no matter what tripod you get though, always make sure that you get one that can support the weight of your gear (plus a little extra for a margin of error). That will make the most difference to how good your photo's and video's look. The tripod has to be able to comfortably support your camera or it will be a bit shaky.