One thing that's really annoying me at the moment is the micro-management you have to do with power lines each time you add a new part of your city not adjacent to any existing buildings (ie. part of the power grid) that you have to run power lines all the way through it so that the starting buildings get the power they need. This could be fixed by making streets act/carry power lines too, similar to SC2013 and the real-world (in Western Europe at least). If a modder is up to the task, I'd love to see something like this.