Know exactly where youre coming from Paul, I think the big problem for most of us is changing to many variables at once, which tends to make it hard to feel any improvement, Ive learnt that carcraft even in a sim is a slow deliberate process, one Im still learning. I have a scribble pad which I use to note the settings I'm working thru, beats forgetting what you changed and by how much.
I always start with the default setup and work that for atleast 10 laps, making note of the corners the car doesnt negotiate well, from here I slowly work on adjusting the car "using the guide" so its as fast and clean through each corner as I can get it , I do this one corner at a time, the trick is, dont adjust to much at once and if it has a negative affect or feel change it back straight away. Sometimes I find when I nail one corner its upsets another, which slows me down, so compromise is also a requirement of the craft.
Then theres some tracks where I just cant get that balance, and theres the challenge, its not beating my opponents that matters most, its beating the track.
Hope this helps someone,
Cheers