I worry some about the risks as I age, but not a lot. I live in a state that doesn't allow a pre-existing condition to be used as a reason to deny insurance, so that doesn't concern me at all. I figure that any kidney disease I might get would have affected both of my kidneys anyway.
My biggest concern is kidney stones. I have a strong family history of it and reported that to the doctors, who saw none in mine and said you can prevent them with diet and hydration.
I too weighed the risks against my recipient's need for it, his discomfort, how it affected his and MY quality of life for him to be on dialysis. In the end, I decided that the only reason NOT to donate would be fear, and I try very hard not to allow fear to stop me from doing anything.
Seeing how well he already feels less than 3 weeks after surgery makes it worth it. I knew he'd feel better, but not so quick.