Shouldn't it be the other way around?
#homer .left-eye { ... }
#bart .left-eye { ... }
.homer #left-eye { ... }
.bart #left-eye { ... } .homer #left-eye
.some-class #some-id makes sense only if you want to style page-unique elements differently in some cases but even in that case I'd argue that #some-page-id #some-id would be better (assuming #some-page-id is the body element id).
In regard to the selector type, does Homer have more than one left eye? More than likely not, but that's why I suggested using all class selectors as an option. Using all class selectors would enable you to produce (a) as many Homers as you'd like and (b) as many left eyes, right eyes, mouths, etc as you'd like.