Likely my tuning knowledge is like yours, all is done via trial-error, before the base line I've tried minimum and mid ride height, the same goes for springs, dampers and ARB's, I've tried to add camber with no success, same with toe, downforce, adding ballast, tweaking power parts and so on, even I've tried an oil change, so you can see with that what's my tuning knowledge, between you and me, don't tell anyone but GT car settings is a mess.
BTW, if you increase rear dampers that will help on neutralising oversteer a bit but if you increase them more than 5 or 6 you'll get too much oversteer when exiting the curve, I've tried it too, I prefer 1/1 rear dampers though.