In the regular part of the Vampires: Bloodlust Elders page, you will see a number of different options for purchasing items with Reward Points. Each option in the Elders costs a different number of Vampires: Bloodlust Reward Points so you have to balance usefulness with cost. Usually trading Vampires: Bloodlust Reward Points for money is the best use.
Refilling the energy bar with Reward Points is a good choice once you have gotten to higher levels where you are more open to leveling up and there are Missions that have a very high financial return.
One unique feature in the Vampires: Bloodlust Elders is the ability to simply buy skill points, which can be very useful for people who want to upgrade their account without the work. This can be important if you have made mistakes during leveling and spent your skill points in irresponsible places. Never use your Vampires: Bloodlust Reward Points to change your identity.