Not sure about heroness, but my recipient and their family have often expressed their gratitude. I downplay it as well but feel more than free to say you're welcome. Always receive a nice Christmas card with gratitude. It was a risk for my family, so I appreciate the thanks from them, but it is not overboard or hero type stuff.
Recently my cousin, whom has PKD, had a donor appear out of nowhere when it looked hopeless. I really appreciate their contribution. So, in a way I get to see it from the other side.
Since it is a choice to donate, not an obligation, it really is a gift. I think it is more than just a casual thing to donate.
For myself, I have had very good health, still do almost five tears later, and my brother does as well. I think we are both grateful.
Cheers