Yeah I think reducing base values, increasing diminishing returns and decreasing the value of sent information compared to retrieved one. I think just implementing a max range on the communications dishes/antennas might also help. Once you get enough power you can just get into orbit/land and spam science, if you had to research better antennas before sending data from mun and farther. What helped me to artificially extend it further is too not overthink things too much, just like actual kerbal science I did all of my flights by trial and error while making at least sure I can return the craft back home. It's definetly a great feature and allows for so much more gameplay to be added besides the sandbox. Edit: As they guy above me mentioned, you've also have to keep in mind the people who are absolutely new to the game and might not even know the other planets/moons exist or how to actually get there. Just an idea that popped into my head, but maybe they could add modified tech trees with increased costs and less/different parts which you can choose from (eg. easy/normal/hard mode with the corresponding tech tree)