If you must, do statistics, machine learning, or "data science". If you are already an experienced dev, a CS or Math degree is not going to give you anything that you dont already have.
Do something multidisciplinary like GIS, you'll learn all the interesting geography bits as well as working with spatial data. It's an interesting field and the technology is becoming increasingly relevant.
Also this is a pretty lazy post. More details than 'experienced dev' would be appreciated