Frank, the poorness of the ISI physics engine is mostly unfounded, its problems are, like any sim, tires. Suspension modelling is more advanced than LFS for example (dynamic roll centres, for one), it also has pretty detailed modelling of diffs, high and low speed dampers and a lot more aero modelling than LFS.
Of course it is not user friendly to change them but as far as the engine goes, its more advanced than LFS.. LFS however takes a more 'dynamic' approach in the tires. In my opinion still fairly wrong in places, but thats where it makes up for some of the other things.
Mind you thats a good thing, aero and dampers are not half as important as working rubber..
Since the base engine in ISI works well until you get to the tires, I'd say fudging and tweaking too much with the good bits is dangerous. Since the only thing that really isn't quite good (neither is LFS or RBR or any sim) are the tyres, that might be an area to fudge a bit..
My 2c anyway, its getting off topic.. Can't wait to see what the hopefully soonish patch for LFS brings.