The garden tour that I've participated in 7 times benefits a battered women's shelter. We do not charge people to see the gardens but have a donation jar at each garden for those who feel inclined to donate. The people who come know the history of the tour and we always have a huge turnout and collect a sizeable amount for the charity.
Yes, it CAN be stressful (on the host gardener) to try and make everything just the way you want it but when people come and see your garden THEY don't see all the perceived flaws that we see.
Like pirl said, the compliments are very rewarding as well as knowing that the donations go to a very good cause.
Our tour board carries a two day insurance policy for the event and we've never had a problem.
By and large, the overwhelming majority of the guests are well behaved and I've never had a problem with kids, dogs, etc.
Having your garden on a tour isn't for everyone, that's for sure. I look at it as a way to share gardening ideas with fellow garden enthusiasts as well as getting new ideas from the guests.
I'm not going to lie. It IS exhausting once it's over and I'm usually hoarse for two days following...kinda like how you feel the day after Christmas. LOL