I agree with you, no human, no matter how deep and thoughtful, could live forever without gettng bored. The standard dub answer (millions of species of animals, plants, etc.) always feel flat for me, for two reasons: 1) what if you're not into zoology or botany? 2) even if there are billions and billions (as Carl Sagan would say) of things to explore, you'll still eventually run out, because billions is still an absolutely minuscule number compared to eternity. Then again, the human mind is finite, so you'd figure that after a while, we'd forget what we'd seen in the past. So eternal life would be kind of like perpetual alzheimer's--doing the same things over again every few billion years, because you'd forgotten that you'd done them before.
What's really sad, though, is that if you ask most Witnesses what they want to do in the New System, they'll say things like 'learn a musical instrument' or 'travel the world'--things they might be able to do right now if they would stop spending all their time on Watchtower BS!