Hi OP. I donated over 20 years ago. I did it because I had completed my family; pregnancy and childbirth had come easily to me, and I wanted to help someone else who had not been so lucky, if I could.
They harvested 18 eggs, and although I wasn't allowed to know the outcome, at my check-up it was hinted that the implantation had been successful. As there were so many eggs there was a possibility of genetic siblings even if not through a multiple birth. It still gives me a good feeling to know that I may have played a small part in someone else having a child, or children. But I know it was a very small part, and I have no sense of 'ownership' for want of a better word, just a hope that it all worked out well for the mum.
I was very open with my family and my children about the donation. I felt that as there was always the possibility the rules would change and any child would be able to trace me, my family needed to know.
I already know that if that happened I'd agree to meet them, to answer any family history questions, and also to tell them what an amazing mum they had, if she was willing to go through so much to have them.
Incidentally I have 2 children, one who looks just like me, and one who is very much like her dad's side of the family. I'm the spitting image of my sister, nothing like my brother. So it's just a lottery.
Whatever you decide, I wish you luck.