I have never made an image that made me say I wish I had a better tripod.
And man-oh-man *so have I...*
In fact it was way back when in my film SLR days that I first decided to buy a "real" tripod, a Gitzo 341... All aluminum, larger than I thought I'd ever need and correspondingly heavy.
And all of a sudden my images were better. A *lot* better...
Several years later CF hit the market with the Gitzo 1348... yes, the same one referenced above; I've had it for about 10 years. At the time, I had trouble justifying the cost (about $600 back then) just to save weight. A trusted sales rep told me it was not the weight that was so important but the lack of vibration. I was skeptical, so he gave me the pod to test out for a weekend...
I went back Monday AM, paid for that pod and immediately sold my pair of aluminum Gitzos.
(BTW that 1348 pod has actually saved my life, but that's a story for another thread.)
In a nutshell, the weight-savings is the bonus... gravy. Lack of vibration is the real reason to use CF.
Oh yeah, and as Jonathan said, the difference is like 60% or 70%, not 5%...
Cheers,
Jack