I think terminals in Delhi should be divided like this -
New Delhi for All premium trains like Shatabdis, Rajdhanis, Durontos, Janshatabdis + Trains towards northern states which are upwards to Delhi like Haryana, Punjab, Himachal, Chandigarh, J&K.
Old...
more... Delhi - For Passengers, MEMUs, Mail express within 300 KMs of Delhi and some Long distance trains towards states like UP, Bihar, Jharkhand, Bengal and NE, and some Superfasts towards Rajasthan and Gujarat.
Anand Vihar - For most trains towards Ganga Valley and Eastern states like UP, Bihar, Jharkhand, Bengal, NE and Odisha
Delhi Sarai Rohilla - For all other trains towards Rajasthan, Gujarat
Hazrat Nizamuddin - For all Non premium states towards Central India (MP, Chattisgarh, Maharashtra) and South India (Goa, Karnataka, Telangana, Andhra Pradesh, Tamil Nadu and Kerala)