Yup. PageRank was magic compared to what came before it, but it can definitely be gamed!

People will do what they can to game GrapeRank. But the contextual nature of GrapeRank makes it more agile than PageRank. My expectation is that in many cases, the effort it takes for the community to counter and neutralize an exploit will be less than the expense incurred by a bad actor engaged in the exploit. Exploits will become less profitable and therefore less of a burden on the system.