As you said, it could upset Saudi and Israel. While it could force the US to pay more attention to Iran, it could also rally the middle east to uncle sam's camp. Not a good idea if China want to pivot to middle east. The US won't even need to spend much of its force, it just need to sell more weapons to the middle east to counter Iran. After all, the US is ready to abandon middle east.

The better way is to deepen economic cooperation with Iran, that's what China did when it sign 400 billions deal with Iran. China could also share some military technology with Iran, to make sure Iran can develop its own weapon that is enough to defend itself.

As for super "Iran" on the American continent, there is no need to search for unicorn. Again, just like with Iran, deepen the economic cooperation with the continent. Once they are tied to China prosperity, they won't be easily sway by the US.