No, a 2-point increase in quant will not lift the overall score by 30 points. They don't release this scoring mechanism, but I'm finding reports on line of Q50, V41 leading to 750 scores in 2009 / 2010, and then later 2010 / 2011 reports of the same score mix with a 740 overall. (Note: if you do this search yourself, there are some posts out there that are bogus - people just trying to promote some service or book. Look for reports from people who do not then talk about how great XYZ resource was. Some of those are legitimate, of course, but some are also fake marketing things where the person posting didn't actually check that certain subscores still lead to a certain overall score today.)
So it's probably more like a 740 today. Possibly a 730 - the quant percentiles just dropped last month.
The next question. Do you need a Q50? :) See this:
https://www.manhattangmat.com/blog/inde ... es-update/If you want it for yourself, or because you think you'll apply for a quant-focused job that will want to see your GMAT score, then okay. But going from 720 to 740 isn't likely to make a huge difference on your b-school application.
If you do take again and get a lower score, the schools won't care. They'll just take the highest score.
So there's no real downside for the test itself. The only potential downside is how else you'd spend that time. If it would take away from time to make the rest of your application package outstanding, then that's not a good trade-off. But if you have the time and feel like you *want* to do this, go for it!