Do we get more out of suffering?

[anagogy]

The more we suffer, do we learn more?

Sometimes you learn less.  Suffering is no guarantee of learning something.  For example, you might do something stupid and burn yourself, and then you do the same stupid thing again and burn yourself yet again.

When we have passed on, will we be more thankful for a life which we suffered more, or less?

Only if we legitimately thought is was the only way to drive a lesson home.  Every soul is different.

Is suffering necessary for spiritual growth?

Nope.  The advantage of suffering is this: when you really know what you don't want, you then become equally clarified about what you DO want (the opposite of whatever you are experiencing).

I consider any challenge to be suffering to an extent, depending on your mindset.

The aversive nature of negative things is a deliberate mechanism of our reality.  Suffering is there as a teacher, but the student does not always listen to the teacher.  Attention to what is not wanted is the ultimate cause of suffering.  Sharp pain really grabs the attention, and helps perpetuate its reality. Whenever you experience something painful, it is an invitation to turn your attention to something better. Just like when you burn your hand, it is an invitation, or admonition, to not do that again.

People think they are doomed to certain circumstances and that things never change.  But the hard truth to accept is this: reality is *always* changing (in our relative illusion).  However, in these circumstances where they appear to not be, it is because they keep changing to the same thing over and over again.  At the end of the day, most people aren't really willing to accept the responsibility of creating their own realities.  It is understandable.  Identity maintains stability by resisting change, because change threatens identity, which is subconsciously perceived as death, something to be avoided.  People fear change for this reason.  People love their comfort zones, even if they are miserable comfort zones.  They have learned to tolerate a certain level of misery, so they keep trudging through it day after day, because, well, hey, its predictable right?

To change circumstances you have to begin by changing your thoughts.  The secret is to make small changes in thinking every day, which will eventually snowball into big changes in what manifests in life.  Affirmations can be helpful in this regard.  

The strongest forces in creation start out as the most gentle currents of thought.

Is it all mindset where you choose to suffer or not?

Suffering is caused by identification.  There is a place in consciousness where everything is just transitory thought: whether it is pain or pleasure, they are not exalted or denigrated.  They become neither aversive, or attractive.  Eventually transitory dualities like that are done away with.  One learns to stand on the river bank and watch the sensation and attach no particular opinion towards it.  I've experienced episodes of it.  When in these states (trance states?), pain is not perceived as aversive.  For example, one time I took a starkly cold shower that by all normal human interpretation would have been shockingly aversive and cold, but in that state it was perceived as "just another sensation".  Not bad.  Not good.  Just different.

I don't want to think that I am doomed to suffer because my higher self thinks it will get more out of it.

You aren't.  If anything, your higher self is trying hard (within the limits of free will) to get you to turn your attention to what is wanted, and thus end your suffering.  Suffering is not exalted on the spiritual planes except to the extent that it serves as motivation for you to tune your consciousness to more harmonious circumstances.