FYI: DisableHostCollapsing is not required when using the site: operator.
A small syntax error with your query is causing the relevancy issue you are experiencing. Try changing your query to the following:
+ "&Query=Cher+%28site%3Aharrahs.com+OR+site%3Acaesarspalace.com%29" |
Also you should remove Web.FileType=DOC from your query unless you are really looking for word documents (which we don't appear to have any indexed on these sites).
Good luck!