I am including 3 images. #1 shows the car I am restoring. #2 shows the fenders and running board as in their original state. #3 shows my touchup work.

The negative is just covered with scratches and many spots, mostly visible with high magnification. Most of the scratches are very faint, but I am thinking that large blowups will be noticable and with so many imperfections the overall appearance may well have a less than perfect look no matter how un-noticable the imperfections are.

I am using the clone tool for all of it.

So my question is, will you look at the images and tell me...
#1 Are these imperfections worthy of hours of repair.
#2 Can your discerning eye detect a difference in the before and after images.
#3 Does my work look like I have a clue what I am doing?

I am concerned that excessive cloning with less than absolutely perfect shades will have a chance of harming the appearance of contours and shading. Or am I worrying over nothing.

Sometimes, heal selections (smart remove) are the better choice over the clone tool, because the selection is then filled with colors that surround the selection, by the pixel range you designate for it. This is particularly useful for smaller blemishes, scratches, etc. It's a lot of mixing and matching of techniques, and then softening. Unless you plan on reproducing these images to poster sizes, I'd say you have nothing to worry about.

Do you plan to print your own copies from your printer? I'd recommend a matte photo quality print paper, particularly for black and white photos.

I have my prints done. I don't see me advancing to the point of buying a super printer. Thats a dream though.

You just explained the heal tool in such a way that I actually understood it. Maybe I'm just so tired that all the distractions in my head are asleep I shall give it a try. Did you zoom in and see all the scratches I am referring to? You don't think they are a problem. I am doing 11x14 prints now and hope to do some a bit bigger eventually.

Thanks for your input. I appreciate it.

I don't see those scratches as a problem, when I use the heal selection. Cloning makes me nervous when covering a broad area of a photograph because no two areas of a picture are identical (unless its solid), even if you selected an area close to your scratch(es).

I just recently repaired an old military photograph for a client that had long scratches cutting through the subject in a diagonal fashion. Using the resynthesizer smart remove (aka heal selection) I selected the Free Select tool and selected the scratches as close as possible, then set my range to within 40 pixels. It worked very well. So well, in fact, on the reprint you couldn't even tell there was ever a scratch.

The smart remove tool is often mis-used and high expectations have been placed upon it in comparison to Photoshop's recent Content Aware fill. I've manage to use smart remove successfully because I am aware of it's limitations and I keep my selection pixel ranges in mind. See http://www.mahvin.com/?p=1849

A good experiment is to start out with multiple small areas to repair, first. Then focus on the larger areas last. This helps you keep your pixel range for selections, more balanced. See http://www.mahvin.com/?p=1182

I've only been using GIMP and resynthesizer for the last 2 years or so, full-time. Before that, most of my work/repairs were done in Photoshop. This was well before Content Aware fill.