Time travelers are clever. You don't have to bring back cheap gold from 2000 BC, just bury it in land you will buy in the 18th century and dig up to day. You could buy cheap items in the 19th century and store them in a warehouse for 100 years until they are collectibles. But mostly you could buy stock cheap in 1964 and sell it high in 2013.
You have a valid point. Vandal Savage, a DC Comics immortal, sold his soul for an end to his eternal bordom. After 100,000 years he was just so old and rich he couldnt even be bothered to bang bitches all day.
Also Lazarus Long in Robert Heinlein's Time Enough for Love. At a point, immortals begin to envy ephemerals.
... "nothing to live for", was so common in that society that the decision to commit suicide was protected by their "Bill of Rights". ...and I'm with LSUTyga73,.. I wanna fly!
My point is, what good is immortality if the world comes to an end? Would you just float around space for all eternity?
Time traveling super heroes need not worry about the end of the world, they just go back to a happy time. An immortal time traveler. That's the ticket. Deju Vu Tujours. You have to be a deity to beat that gig. Son-O-God.
There are other worlds and universes to exploit. During the entire course of humanity you have time to figure out how to go to an alternate earth in a mirror universe or a planet where the aliens look human.
