Alpha Centauri is simply a weird earth. I think that a game around long-lived creatures that colonize a galaxy and have to work with relativistic effects could be different and fun. At some level it builds on all these different ways of looking at time. Breathe some life via simulation into this tongue-in-cheek interstellar economics: https://www.princeton.edu/~pkrugman/interstellar.pdf
They will not have to work with relativistic effects. Nobody is going to fly faster than 0.1C. It is prohibitively expensive energy-wise and there is no point of doing that. Just accelerate to 0.01C, and arrive at the neighbouring system in 400 years. 400 years is a blink of eye, anyway.