The weirdest thing about the "I don't like sand" line is that I can really understand why George Lucas must have thought that the line would work.I could name more than one (at least to me and some others) iconic track that I can immediately call to mind originating from any of the Lucas films, even if not on the same level -- "The Emperor Arrives" from Return of the Jedi, "Anakin's Betrayal" from Revenge of the Sith and "Across the Stars" from Attack of the Clones (one place where John Williams' music, no matter how brilliant, really only can do so much; "Across the Stars" literally played across a total lack of dialogue and imagery is better than what actually exists in terms of portraying Anakin and Padmé's tragic love in the films) to name the first that I can call to mind. There is no such for me for the sequels. That may be because even the most recent of the old films came out half my lifetime ago and they've had time to percolate with me while the sequels are all fairly recent, but I'm not sure I buy that -- certainly not with the top ones.
Padmé is talking about her very idyllic childhood, and when she mentions sand, she mentions it as one of these small things in life, the little details that puts an extra richness to everything.
Anakin, with his reply is not just communicating, but poignantly reflecting on, that he cannot relate to it, subtly bringing attention to his very tragic childhood and how his entire life has been a constant struggle. He mourns the loss of a childhood he never had, is also in a low key sense acknowledging of his stunted emotional development.
Anakin may have complained about Obi-Wan before (and admittedly it didn't make him look good doing so), but other than that, most of the conversation has been about Padmé's life the past ten years, and when Anakin is talking about how Jedis cannot love, he approaches the matter in a very theoretical matter. When Anakin says, "I don't like sand", he is letting his guard down, he is opening up.
The line probably could have worked had the love story in general been handled better.