barkeeper's friend is probably cheapest at wal-mart or target, around $2-$3.
rubbing alcohol on cleaning clear soles on vi's and xi's- i don't know if this will hurt it or not. i just clean the clear parts of these shoeswith shoe cleaner and then use sea glow.
sea glow on back tab of iii's and toebox of vii's- NO! you're just gonna ruin these areas if you use it. for the back tab of iii's, i use mrclean magic eraser. for the vii's, depends on how bad the toebox looks. just light sanding to take away the yellowing.
ds xi's and using seaglow- go ahead and clean them up with seaglow. it shouldn't hurt them since the yellowing shouldn't be too deep.