I love to play Haunted Mansion with friends, although Gamebot, DarthJordan and HauntedGrim all know how bad I am at it! lol
I think it is selfish to try and get more credits by being by yourself, and having another person with you means that you not only get thrashed by the other team, you can rely on them when you need them.
I think it would be wise to do what they did with the pirates game and have computers to fill in the missing spaces, that way people who try this sort of thing will get nothing out of it as the AI dudes will get all the ghosts before they do!
Also, you should only boot if you want to play with a couple of friends. When I was playing with the three mentioned above about 50 billion people were trying to get in our game, even when we said no.