There is a sound editor, and I tried directly copying the F1C files to GP4. Result: a disaster. There's more than the basic 4 enigne files I think, but also there are notepad files controlling how the sounds sound, and they are what make the F1C sounds sound bad I think. They are easily editable, but it needs a lot of playing around with to get it right, and I couldn't do it!!!
I don't think people will bother with new F1 sounds, they'll just do it for the 'Mods'.
But the GP4 sounds aren't great (as you've said) after you've played F1C. They lack a certain punch, and they sound a bit too high.
Let's hope!