regarding A: i am not a good example. with B.Sc. in math i invested 100% prep time in verbal, except prep tests (in which i did both). i decided to do it after my first Gmatprep in which i found out that i have no problems whatsoever in the Q section...
which brings me to answer your B question:
given your very average scores, i think that your score is low because there are some distinct areas of weakness. i.e. not erros to overcome but material you should be more familiar with (which eventually results in error).
because of this i'd suggest to leave OG alone for some time. it doesn't help you. it is not "area specific", but a collection of "all around" questions. first you should i dentify your weaknesses by area/skill, then find a book that cover those areas, and improve your skills gradually. only then return to OG to master the "art of getting the question right when you know how to do it"