As Justin says, "the fall of man" is a major, major issue.
Not that any individual sinned and thus brought sickness upon themselves, but that the Fall brought it upon the whole of creation and we are still living with the fallout.
Sickness is not God's plan.
I agree He will still bless us during it, He will work through us while we're sick, He doesn't accuse us or curse us.
But He doesn't desire it for us - He wants us whole, and if we're not, it's only because we live within the physical and temporal constraints of the broken world.
At the end of time, all will be healed, and at that time all will give glory to God.
As for the "benefits," spiritual or otherwise, of sickness, I can never see how my depression might have been a good thing, no way.
It distorted my self-image, my image of God, my relationships. How can any of that glorify God or enable me to know Him and walk with Him and reflect His glory?
The only good thing that might come from such a thing is the empathy and support I can offer others who suffer depression, but there may be better ways to get to that, and in any case, if all of us could receive full healing there would be no need for that kind of ministry.
God bless, love Sue