This is just an idea, I'm not planning on implementing it anytime soon, but what do people think of the idea of varying a cost multiplier by geographic location? Imagine that at sim start up, there's a function that determines how costs vary accross the sim. It could be simple such as high costs to the left, lower costs to the right, or much more complex such as a random "cost density" or ribbons of lower costs flowing through the sim. This cost landscape could be made visible by modifying the blue background picture to show areas of higher costs and areas of lower costs, say by using darker colors for higher cost. It woudl be super cool if bots could detect this landscape explicitly.
Just an idea. One could imagine bots becoming territorial and defending an oasis of lower cost, storing up nrg to cross a desert of higher costs, getting smart about navigating so as to try and stay in the valleys of low cost, etc.