maybe finding a tire with a different sidewall structure? not sure what your using or etc.. but a lot of tires have reinforced sidewalls, which absorb less imperfections..
changing out the springs and shocks will make your *** feel better, but will not help transfer to the steering wheel, if you know what i am saying.. so assuming you have the same power steering set up as the rest of us, i agree it is a bit sensitive. it does feel different lowered though, i wont say it will improve what you are feeling, but the steering wheel is a little less shaky sort of..
did your toyota crown (model name i am unfamiliar with) have rack and pinion steering? i assume it does as it looks like our cressida into a lexus line here. but that car also possibly with the extra weight and luxury suspension, it would be tough to get the aveo similar..
you could pour 2" of cement in the entire floor board?