For me, I'd rather find out about stuff I don't know about, rather than what I do, if that makes sense.
No one in my family showed any signs of Alzheimer's, for instance, although my mom showed some forgetfulness in the last couple years of her life (91 when she died). Might be good to know, so hubby and I can think through living arrangements and that sort of thing sooner rather than later, if necessary.
My grandfather died of a brain tumor in his early 40's. If that sort of tumor is genetically relevant, also might be good to know.
My hearing - well, it's down around the severe/profound area. No one else in the family has any hearing loss. So, good idea for the nephews to get checked out genetically, or not? I'd put my money on "not," considering everything. And certainly "not" for me, it wouldn't make any difference now to find out there's some defective gene in there.
It's amazing what we can find out by genetic testing, but how much money, time and effort are worth putting into it to find every possible thing, I don't know.