Christian, do not think that trying to find out what Nibbana is is merely baseless and meaningless speculation.
It is true that until we ourselves attain Nibbana, we can never truly experience it for what it is. However it is important to have a roadmap (the Fourth Noble Truth) and to have at least a somewhat limited understanding of our destination (the Third Noble Truth) if we are to motivate ourselves to pursue the goal of Nibbana.
So long as we do not spend our whole lives speculating wildly about the nature of Nibbana, but instead put in effort to be mindful of our thoughts, speech and behaviour, as well as in learning Dhamma, we would be making productive and wise use of our time.
So many people turn away from Buddhism because they do not truly understand its important message or else they are misled by pseudo versions of Buddhism, and wonder why they do not feel very much different afterwards. They very much need to know what kind of reward they can expect if they were to adhere to the advice of the Buddha.