[Princeton Review's LiveGrader]

You might check out Peak Performance's GMAT or GRE writing course for help on the essay section. They offer personalized feedback for 4 practice tests and helped me raise my score from a 3.5 to a 6! The course is live and online and is offered monthly, I believe.

[essay lengths?]

From what I've read about computer scored essays, word count does matter. On the SAT, for instance, there's been studies that show longer essays receive higher scores and length was one of the most critical factors.

[ScoreItNow for Analytical Writing section worth it?]

Does Score It Now make you write an essay on one of their questions, or do you get to submit a practice essay that you did on your own already for scoring. If it is computer scored, I would imagine it is one of their essays, and then it all boils down to whether or not their essay questions accurately reflect the GRE essay questions. If not, I wouldn't waste your time or money and a low score wouldn't necessarily even be an accurate reflection of your ability.

[Any advise of low verbal score]

I really don't think flash cards will help that much, unless it is strictly vocabulary that accounts for your lower verbal score. But it sounds more like the problem is reading comprehension, which is in part based on vocabulary but also your ability to identify the main idea of a paragraph. Also, vocabulary won't really help with sentence correction section, which is all about grammar. Rather than working with flash cards, I would read the paper and magazines daily and work on creating 1 sentence summaries of each paragraph (even if only in your mind).