Irule to redirect traffic based on path and uri

Why not use the switch function for it all. I believe the switch command uses the first match so you could do:

when HTTP_REQUEST { 
  switch [string tolower [HTTP::uri]] { 
            "/bla/blabla.gif" { pool pool-frontend }
            "/bla*" {pool pool-frontend2}
            default {pool default}
        }
}