The scene reminded me, oddly enough, of the end of the first act of Peter Pan. In J. M. Barrie's play, Peter Pan sacrifices himself to save Wendy. As they're trapped on Marooner's Rock with the tide rising, Peter only has the means to carry one of them off to safety.* He chooses Wendy and stands alone as she flies to safety. The line that sticks with you is Peter's thought that "to die will be an awfully big adventure."
Data's personal transporter pixie dust may be much higher-tech, but the parallel is there. For him, though, I don't think there's anything beyond that moment. We might debate whether or not Data has a soul, but let's assume, for the moment, that he does not. There is no "awfully big adventure" awaiting him. There must be something else, then, that makes his death meaningful, and that "something else" has everything to do with his quest to be more human.
Death is a part of our fallen human condition. Being mortal and finite is, at least for now, part of what it means to be human. More important still, how we go to our death, and how we accept it, also define us.
Earlier in the movie, Captain Picard quotes St. Paul (from the KJV) in saying, "For now we see but through a glass darkly." (1 Cor 13:12 NAB) If he continued to the next verse, he'd say "So faith, hope, love remain... but the greatest of these is love." (1 Cor 13:13) That is just what these sacrifices are about: not just adventure or bravery but love. Love ("caritas" or charity) is the greatest virtue, the one that was and always will be. (1 John 4:8) One might say that the more love we show, the more human we are.
To Peter Pan, death is one more adventure to have. The boy that won't grow up may lack the spiritual maturity to see, or at least admit, the love behind his sacrificial act. The android that never becomes human, however, shares the love in his sacrifice in that last look between him and Picard. He finds in his last moments the perfect expression of humanity; he is, in the end, Christ-like.
"No one has greater love than this, to lay down one's life for one's friends." (John 15:13)* I've seen reference online to Wendy's kite, but all the staged versions I've seen involve Peter having just enough pixie dust for one of them.