Don't expect to make money on your per diem. It is not meant to supplement your salary.
In taxed countries, companies will provide higher per diems since they don't pay social charges on them and employees don't pay taxes on them (everybody is happy!).
In the UAE, every money they give you (or service providers in the country) gets recycled and ends up in the royal purse. Not so with the off-base per diems which is money gone forever...and they are not happy. Spinneys, Costa's and MMI are managed by EK and they do have inflation so don't think the management negotiates 0% inflation in hotels for you...