Very good points.
I agree that Buffy's lack of showing up entirely affected everything. If Buffy hadn't shown up, Willow would not have "seized the day" although Jesse probably still would have made off with Darla. I agree with Jules on the fact that Jesse most probably wasn't vamped, because as Luke said (paraphrasing here 🙂), "You've been upgraded from a meal to bait." There would be no reason to use Jesse to lure since theres no Slayer there.
On the issue of Cordelia not being eaten by Luke. Now thats a tricky one! Maybe she never showed up because the previous night had been lackluster, I mean the whole Buffy-attacking-her thing was apparently the highlight of her night. I doubt though that Giles alone (because he never would have been formally introduced to Willow and Xander as companions without Buffy) would have faced Luke or any of the vampires. Angel is a feasable opponent, but at that time he was more afraid than willing to fight. Buffy was the one who brought out the fight in him.
Or maybe Anyanka had to change a few things, because Cordelia came to the Wishverse on exactly the same as it was in the real Buffyverse, so possibly Anyanka changed it so that Cordelia would have survived 'til that point so she could see what her wish granted her. Without Cordelia being able to see what Sunnyd would be like without Buffy, then Anya's wish would have been wasted, since it was catered to Cordelia.