Noone will care if your second test is above 700 what your first test was. Schools specifically state that they only consider the highest score. I can only see them having issues with multiple scores only if you show a declining performance. Lets say you got a 710 and got 600 and 580 in subsequent tests, indicating that the 710 may be a fluke.
Yeah, general consensus is that
MGMAT is good to refine your quant, not that helpful for verbal. Lots of posters mention rocking the verbal for MG and getting a much lower score on the actual test. Don't think too much about practice score results other than GMATprep. The CATs from Kaplan, Veritas, Knewton and all the other big names frequently have very "iffy" algos to determine scores. This is not to say its not useful to take the tests as it'll help you with question exposure and time management. Just take the score with a pinch of salt.
I don't think a class is necessary in this case. A class would be most helpful if you need help with your core fundamentals. Its not clear that you have a problem there especially given that you had a situation where you had to
guess around 1 fifth of the test.... well, I think you need to work on test taking skills. 1:40min for SC/CR, 2:30 for RC. STICK TO IT. You can go over, but you have to consciously make up for lost time in subsequent qtns. Remember, if you're guessing towards the end, that means a high likelihood for a string of successive wrong answers. Guess how much the GMAT penalizes for that kind of error profile. A LOT. I think you prob ran out of time because you got hung up for 1 or 2 qtns. 8 to 10 minutes fly by when you're engrossed in a qtn. I miss the last qtn in my quant on my actual gmat because I got engrossed with double checking qtn 37 which I was 90% confident of. And I had 9 minutes to work on it. I didn't even know the timer had run down until the screen suddenly changed to "your time is up"
But if spending a few hundred on a test just means a movie instead of broadway for the weekend or foregoing that must have jimmy choos or true religion jeans, it won't hurt to take a course either. Just make sure you focus on time management as well though.
Study smart, study efficiently. And Good luck! You're going to rock the test.