“Why should Hashem’s will have any intrinsic value?”
Because Hashem is Perfect, HE is just, HE is generous and HE knows what’s best for us. So by definition everything he tell us to do has to be beneficial for us and for HIM.
We have to realize that we are ONE with Hashem so the mitzvahs aren’t just for HIS benefit it’s for ours as well.
Doing mitzvah is beneficial for us (sachar) in this world even if the reward (pras) will only come to us in the next world.