"saying there is no need for a rocket capable of lifting a 1000 ton payload is like saying there was no need for diesel turbines when we were using clipperships.

More like there is was no need for the Titanic when we were using clipperships.
First thing is you need at least a prototype engine which works. Once that happens you can maybe build a engine that work in space. If you can then make one of these engine lift it's own weight, then maybe you can improve it so it would work to lift payloads off Earth. At this point there is no known reason why it needs to be so huge, why not make smaller? Lift 100 tons payload? This is still bigger than is needed.
What is needed is lower costs of lifting payloads into orbit, not huge payloads. Your house probably weights less than 100 tons. A Nuclear rocket which could lift 100 tons to orbit, cost say 5 billion to build, cost say 5 million per launch, would get us to Mars or wherever.
10 nuclear rockets that can lift 100 tons each will be cheaper than build one nuclear rocket that can lift 1000 ton. 20 nuclear rocket that can lift 50 tons would even be cheaper.
When launch prices get down to around $10 per lb or lower, then maybe there might be some need for some huge spaceship- maybe there some need to transport whales to Europa or something.