Yeah you are of course right regarding Cassian himself, and it's certainly suspensful to see how exactly they get in/out. though at least in the 2nd arc I'd argue that it's also interesting to see if they succeed or not. The money is a huge mcguffin, but it's also one that the rebels can live without. Normally in star wars they steal something or someone that is important to further the story, but the money basically doesn't matter and we see it not having any tangable effect on the rebels (though of course the heist increases the activity of the isb). That makes it unclear if they will even succeed. On the other hand there are a bunch of characters that conveniently get introduced so we can fear that they might die. And the do die.