I think you're right that it's definitely something that you want to fix. It's bound to break something at some point if it's slamming shut too hard.
If you're handy, I would lean toward buying the stays from IOS
http://www.everythinginfiniti.com and doing the work yourself. The "lift cylinders" as they're called on the site, are about $187+ shipping, but they only show one style, so I'm not sure if they would be stronger than the ones that are already on your car.
Remember that the only way a dealership tech. can make $$$ is to beat the clock by doing the work in less than the book time you're paying. On the other hand, you can take a full weekend to make sure it's perfect if you want.
The FSM is available at
http://www.phatg20.net and should be pretty detailed on the correct method of removing the rear seat.
Good luck!
Heath