I don't see how this gateway to Mars or the Moon could be useful. In the current situation, this will always increase the price. A space dock could only be useful in two cases:
1. If you're building a big spacecraft which can't be lifted in one piece.
2. You're launching to and from that space dock multiple times, without going back to the Earth.
3. You're building in space from materials taken from asteroids.
Arguably, you can build the bigger spacecraft without help from the station – a station as we can build it now doesn't provide that much help, and nobody is launching interplanetary spaceships on regular basis.
What am I missing?