Yes I agree with you, Dumbledore could have spoken to Snape about it, he didn't. I don't think that equates to plotting Snape's death.
Let's say that Dumbledore did destroy the Wand and he told Snape. Would Voldemort have believed Snape? Would Snape have left that information lying about in his mind, or would it have been safely tucked away, hidden by Occlumency. The fact that the Wand existed was found out by Voldemort by following the trail. It led to Dumbledore and onto Snape. Dumbledore could never have Obliviated everybody who knew about it and Ollivander was well beyond his reach. Would Voldemort believe for a second that Dumbledore had willingly destroyed the most powerful wand in the world? I rather doubt it, he would have killed Snape anyway.
As I have stated before Dumbledore needed Snape alive. He needed him alive and in a position to know when Nagini would be protected by Voldemort. As we now know that did not happen till the middle of the Battle of Hogwarts. It was a very fine line and I think Dumbledore knew and apppreciated the danger Snape would be in, but there was nothing he could do to really lessen that danger. Both he and Snape knew Voldemort had to be stopped at all costs and give Snape credit where it is due, he put himself in harm's way to get to that end. Yes Snape stood in the line of fire, he was a soldier in a war against a great evil. That's what soldiers do, they stand in the line of fire.
The blame for Snape's death lies at Voldemort's door, no one elses. He started the War and Snape helped finish it.