When things like that happen the governments of those states don't genuinely believe it was Iran. They know it was the US/Zionists but they go along with blaming Iran because it's currently more convenient to use it as a pretext to agitate against Iran and gain "good boy points" with the US. Some of the population may be fooled by the media but the governments have enough intelligence capabilities to recognize false flags.

If they genuinely want to get out from under the US thumb and establish a mutual understanding with Iran for regional stability and security then they will have to start calling out the real culprits.

That is how you will know if the agreement was signed in good faith or not. Whether the Saudis are willing to engage in good faith that i don't know.

Simply not having US military stationed there is already a huge victory in itself, or am I missing something? Ultimately, Iran wants zero US military presence in the region, and this could be a major initial step in that direction. As long as Iran keeps bombing US allies and leaving be the neutral states, it sends a powerful message.

What can Saudi do or provide that US and Israel don't already have in spades?

Basing locations. Geographical limitations are a reality. If you cannot launch attacks from close by your options will be much more limited. If only a few of the Gulf state comprador regimes remain available to them in that region, that significantly reduces their tactical flexibility and shrinks the area to disperse/hide their assets over.

Taking Saudi Arabia out of the equation is a net advantage for Iran. There are still plenty of targets in the region without them.