It was *definitely* worth it for me to get two points higher on my third try (163, 166, 168). Money went up 10k per year at my target school. I was already admitted with money, but they reexamined and upped it. That's 30k I don't have to worry about due to two freakin' points.
I had no hard evidence that I could do better, but felt like I had a reasonable expectation of doing better. I didn't get my target of 172 (alas, I screwed up on my strength, logic games, and had to guess on about 5 questions there), but apparently, 2 points make a big difference anyway.
I considered just sticking with what I had. I was already in at my target school. But I went ahead again because the small investment (relatively) had such a huge upside. I mean, if you consider test fee, prep materials, vacation time used to study, and incidentals, it still only amounts to maybe $1,000 (probably way less). That's $1k and sweat for a $30k return.
That logic games section will haunt me (170 was in my grasp!), but still, 30k is 30k and it's at a great school. I'm glad I retook.