He will put extra bums in seats as he has a fan club that will travel to see him but as people have said Windsor is very popular and always well attended regardless (being a straight run in on the train from Waterloo with a riverboat ride if you are inclined) so not overly difficult for Londoners to go especially as it is rather nice down that neck of the words especially if the weather plays ball.
Kempton will get a bump in attendance for sure and probably a dedicated camera tracking him, which will at least show that there are people actually in attendance, which is not always evident when cameras are usually there…..I do wonder whether they purposely don’t seem to have cameras pointed at the grandstands during A/W meetings to hide the fact that not many people are there generally.