Sure the Hammer does serve some importance, but with portals/time travel you can go to any point in time and find a hammer. You could get millions of hammers. Time travel is a whole aspect that some humans believe can't happen, it can, we just need $5bn worth of grant money and a very large testing area. The hammer is lesser. It served its purpose to evolve into greater tools. Why use something older when there is something new to be done. Progression that is what humans are here for. To live alongside nature and to progress to weld the two together to make the world a better place.
If we made the time machine and do the littlest thing to the future continuum like in your argument for example 500 billion hammers that would change the future somewhat catastrophic failure in the time the future would change if we went into the future to fix the hammers it would cause failure to the Past, Present and Future I mean if you wanna die sooner than later then just keep the hammer's you already got and be happy with it.