Sirs a Corolla is better in fuel economy by nearly 10% wether its a XLI or Altis, A/T or manual.
So whatever amount of mileage a Civic will return, Altis will better it considerably.
There is no point of buying a car simply because you have not owned one or to not buy a car since you own one.
I will definitely not buy a Camry if I already have an Accord just for the sake of change or a Lexus IS because I have a C180 already standing in my garage, but that is only me, everyone has his own perception.
BTW, the poster has not gave any feedback yet about his decision.
Regards