You can see a good comparison between the two lenses at Ken Rockwell (Review)
His summary is
I just got one of these to compare against the 24-70mm f/2.8 AFS. The good news is that this lens, Nikon's flagship professional midrange zoom of the 1990s, has pretty much the same optical performance as the AFS lenses on a D3, with a lot less weight. As of 2007, this 35-70mm is also available at a bargain close-out price of about $470!
Of the sharpness of the 35-70 he says
Sharpness is great.
It's sharp in the center at all settings.
On the Nikon D3, it's a little softer wide open in the corners, and sharpens up a stop or two down. Even wide open it's pretty good and much better than the cheaper zooms.
Compared directly to the $1,700 24-70mm f/2.8 AFS, the 35-70mm f/2.8 is only a little softer in the corners wide open on a D3. This is only visible by setting up a deliberate test where the corners have subject material that will be in perfect focus at f/2.8 and then looking at the images at 100% on my monitor.
On film, I doubt I'd see any of the corner softening even on tests. It's only visible deliberately shooting from a mountain top at infinity, so that there are details to see, in focus, in the far corners. Real subjects we shoot at f/2.8 aren't flat like the Earth, so I've never seen this in anything but deliberate test photos.
On the other hand you should see the SlrGear.com review of 24-70 lens
The results are singularly good. This is an outstanding lens.
I reproduce one graph below from the SLRGear web site. I leave it to you decide whether the results justify the higher price.
Note the unusual measure of sharpness, the Blur Unit. You can think of this as one Blur Unit being very roughly equal to the blurring of an edge by one pixel. One Blur Unit is about as sharp as you can get.