I dunno. That's a tough question. Here are some stabs:
1. Confidence
You can gain confidence without suffering. For instance, solving a difficult puzzle doesn't involve suffering but would increase confidence.
Do people have more trust in God after suffering greatly or less?
3. Personal validation of what you've been taught
How would this be useful if suffering didn't exist at all?
4. Ability to teach others how to overcome
Same issue -- how is this useful if others don't
need to overcome?
Also, although there won't be calamity per se, or even temptation, I think that we still have the ability in the next life to choose to do evil. So the ability to choose wisely when the option is presented to us is valuable.
If God can set heaven up where we can choose to be evil but there isn't calamity, then why does this world have calamity? If your premise is true, the calamity is extraneous. Why does it exist?
I took philosophy and there was this question of whether God cannot do evil because he is God, or if it's because he is God he never does evil. It was supposed to be a circular question that defeated the possibility of there being a God, but I just think that God could do evil, but chooses not to, and that if he ever did, he would cease to be God. Although we may not be God in the next life, I think it will be similar for us. There will still be choices to make, and now is the time for us to learn to make them well.
The problem you're referring to is known as Euthyphro's Dilemma.
If what God commands is good because God commands it that's called Divine Command Theory. But then if God commands you to punch an infant in the face that would be "good." I've also shown in another thread elsewhere that Divine Command Theory is epistemically untenable.
The other horn of Euthyphro's Dilemma -- that what God commands is good because it is good -- implies a higher transcendental morality that even God Almighty obeys. Where did that morality come from if God is the creator? That's the dilemma. It's a logical contradiction unless it's admitted that God is contingent on higher transcendental truths, which most theists find to be an unacceptable assertion.
If God is contingent what exactly does His existence "explain?" Not much... the "explanatory power" of a creator-god goes up in flames if God is contingent. Not that I would agree god-explanations are explanatory whatsoever, but that's beside the point right now.