Oh, I totally understand limiting the number of kids. I wasn't even mad that they didn't invite her. I was mad that their little game rubbed her nose in it. And that the mom was clueless that bringing members of the party over to our house might hurt my DD's feelings. So, I would recommend that if the DD has friends on the street who are not invited to the party that they skip the scavenger hunt.
BTW, I am writing down all these ideas! We're having a beach party for my DD's 9th birthday. As long as her BFF gets over the idea of dead fish in the lake, LOL!