VQuick
There are some of the less popular cars that I like, and I don't want to trouble someone by requesting setups for them all. Examples include the Datsun 510 and 240Z, Toyota TA22 Celica, etc. Ditto for certain FFs, MRs and AWDs.
Any ideas on a general, 'one size fits all' setup that could get me started?

I figure a baseline setup like that is better than nothing.
One size fits all huh.... OK, I'll try... However, I am redoing the 24hour Nurbringer in B-Spec with a Saleen right now, so I have to do from memory... (putting miles on Saleen before Saleen race for more spec points).. And to get another F1 car!
OK, shakey memory, so bear with possible mistakles in naming...
Using the Full Custon Suspension, look at the defaults of the first setting. Note that they are a ratios, usually 2x the botton setting. I move them both so the larger is near the top, but not maximum, and then set the smaller of the two to the same multiple of it's lowest setting. Example... Front/Rear default, 6.4/5.8, lower settings front/rear 3.2/2.9, max setting 15 each. I would simply double each to 12.8/11.6, however, if I multiple each default by 4.4, I would set them to 14.1/12.8.
OK, Bound and Rebound.... I almost always leave the front and backs to 6 for the upper pair setting and 8 to the lower pair.
Height.... Except for tracks that are rough, I set the height to minumum. The rougher the track, the higher you must set the height.
Bottom Setting, I almost aways set the Stabilizer to 6.
I usually set the camber to 4 front and rear, and the toe to -1 rear.
I have found it unnecessary on most tarmac tracks to deviate from this method. GT4 is less sensitive to setting changes than GT3 was.
Now ballast.... It helps acceleration, normally, on high powered cars, to add ballast over the drive axle. I got something like 1 sec better on the 1/4 mile with the TVR Speed 12 by adding 200KG to the rear axle. On most MR and FR cars, adding weight over the rear axle will balance the car, and give you better traction.
Another thing ballast. Besides adding weight and increasing spec points won, FF and FR cars likely have more weight over the front axle than the rear, and spring setting higher in the front because of this. I think the default spring settings are proportional to the cars balance. I sometimes add ballast to the 'lighter' side, then match the spring rates. The cars generally corner better when doing this.