You’re right in your advice on how to prep for the GMAT...however...

I used to do offsite alumni admissions interviews for my b-school (top 5-10 in many rankings), and the instructions I had were as follows:
1. If a student’s GMAT score is in the top 60-70 percentile, it is assumed they can be successful in the classroom, and that’s what the GPA and GMAT are used to determine. If you’re in that range, you’re considered academically acceptable, and your scores are set aside.
2. It’s then all about finding interesting and engaging people who have done something noteworthy and will likely do something exceptional post MBA. They weren’t looking for a class full of quant stars (even though it was a finance-heavy program). They wanted people with an ambitious story from their 3-6 years of post-college pre-MBA years.

The best thing an undergrad can do to make themself marketable to a top MBA program is to go out and start a business, take a risk, try to save the world, etc. Most of those people happen to do quite well on standardized tests, but that’s not the key.

Just my thoughts.