If we expect no reward, does that not mean we truly don't believe His word. The bible is full of promises of reward. The greatest reward is of coarse God himself. But if I read this correctly (and I may not have) to try and take action toward God with no expectation of reward from him whatsoever is to try and take action with disinterest. I desire to do the good that the bible commands simply for just that the promises of the bible being revealed.
Ps 37:7 PS 145:19 Mat 6:33 Each of these verse have promise in them. And each one has a command in it as well. Our focus should be on the command not the promise. Focusing on the promise to much creates bitterness when things are not going well. However focusing on the command and believing that the bible is true and we can stand on the promises is key to a enduring faith. When you stand on a large rock playing king of the hill you do not focus on the rock but on the task of holding your position on the rock. Standing on the promises of God is much the same as that battle. The world,satan, and flesh wants to take us off the rock of salvation (aka biblical promise) Do I expect that God will give me all my wants. No. But I do expect to receive my desires. And since the bible says that our heart is renewed, I will conclude that wants are much of the time fleshly and real desires align with what God wants. The real hard part is knowing the difference.