Yes, the 24-70mm f/2.8G is generally the better lens overall, but the upgrade may or may not be worth it depending on your needs.

From the answers provided:

• Autofocus: The 24-70mm uses AF-S, which is generally faster than the older AF-D design.
• Low-light: Both lenses are f/2.8, so light-gathering is essentially the same. The newer lens may focus more confidently, but exposure performance is not inherently better.
• Sharpness: The 35-70mm is still regarded as very good optically. Reports in the answers suggest the 24-70mm is only a little better, not dramatically sharper.
• Vignetting: No strong evidence was given that this is a major deciding difference.
• Range: The biggest practical advantage is the wider 24mm end, which is much more useful than starting at 35mm for many photographers.

So: if you want faster AF and a much more versatile wide end, the 24-70mm is a real upgrade. If you're happy with 35-70mm coverage and strong image quality, the 35-70mm f/2.8D remains a capable lens and the improvement may be modest for the cost.