No I wouldn't argue against Star Wars being influenced by Dune, like you I love them both, but I would say also that Lucas had to have the bulk of his ideas before being exposed to Dune, conjecture, I know. To be sincere I would probaly be very dissapointed though if Lucas came out and said he was very influenced by Dune, (lets be clear, I mean the book, not the movie, because well the transition was mediocre)
As for 13 I would say that the point being that Anakin never really know definitively what happen to Padme, I'm sure he knew of her death, being force sensative, but the fact that she must have rejected him futhered his descent, not caused it.