I think Americans would use the Past Perfect in the given sentences, just like Britons or any other English speakers would. Otherwise, the meaning of the sentences would be changed.
We use wish with the Past Perfect when we have regrets about the past:
I wish I hadn't taken your advice. (but I did)
I wish I had known you then. (but I didn't)
I wish he had let me know that he was coming. (but he didn't)
I wish I hadn't splashed out on that car. (but I did)
We use wish with the Past Simple or Continuous to express regret about present situations:
I wish I was taller. (but I'm not)
I wish I was going on holiday with you. (but I'm not)
I wish you were more help. (but you are not)
Both of your sentences are about regrets about the past. So, it wouldn't be correct to use the Past Simple instead of the Past Perfect.