Aside from someone who does heavy video editing or photoshop.....I doubt anyone will notice the difference between having 8gb vs 16gb in the next 5 years. I mean you can get away with 2gb on mountain lion
I would have to disagree because I'm running 4 apps plus whatever normal background processes maybe running and I'm using 1.18 GB if you had 2gb you don't have much left to multitask 4 should be at least minimum. Maybe to an everyday user 8 - 16gb is't noticeable but to someone as you said who does heavy video or photoshop editing or likes to run multiple CPU and RAM intensive apps at once then yes it would be worth the upgrade. And in the rMBPs case it is not upgradable.