Although I agree with almost all of your interpretation (God is sufficient), I'm not sure about the "thorn". After all, Paul seems to be referring to HIS weaknesses, not those of the people he encounters.
Granted: I am not a linguist, but...
The NIV renders the word for exalted as "conceited", so Paul is saying that the thorn was given to him to keep him from becoming conceited. (Likewise, the NASB renders the verse as "exalted myself").
Also, the word "infirmities" in the KJV and the NKJV ("My grace is sufficient for you, for My strength is made perfect in weakness." Therefore most gladly I will rather boast in my infirmities...) are rendered as "weakness" in the NIV and the NASB ("My grace is sufficient for you, for my power is made perfect in weakness." Therefore I will boast all the more gladly about my weaknesses...).
So the question here is: Is the same greek word used twice, or is a different greek word used in the second part of the sentence? This doesn't really change anything you said, just an interesting note about why people think of it as a sickness.
Personally, I always saw it as a physical limitation (an almost literal "thorn in his flesh"). I mean, after all:
"I have worked much harder, been in prison more frequently, been flogged more severely, and been exposed to death again and again. Five times I received from the Jews the forty lashes minus one. Three times I was beaten with rods, once I was stoned, three times I was shipwrecked, I spent a night and a day in the open sea, I have been constantly on the move. I have been in danger from rivers, in danger from bandits, in danger from my own countrymen, in danger from Gentiles; in danger in the city, in danger in the country, in danger at sea; and in danger from false brothers. I have labored and toiled and have often gone without sleep; I have known hunger and thirst and have often gone without food; I have been cold and naked. Besides everything else, I face daily the pressure of my concern for all the churches. Who is weak, and I do not feel weak? Who is led into sin, and I do not inwardly burn?
If I must boast, I will boast of the things that show my weakness."
It's not so far-fetched to imagine that he had some physiological repercussions from this kind of life. Maybe a limp?