I'm sure there is a bit of variety here, but I don't mind if less than 100% goes to charitable work.
I've often donated / sponsored for walk-a-thons and such things. The person I give to usually gets lunch and the like so some of my money is going to them. Sometimes the person has had to kick in and sometimes not. I have given to multi-day events where the participants get bused back to the start, get meals, etc.
Yes, some of my money went to that administration and support. But some of my money goes to similar stuff if I just give it directly. Many organizations run 50% and more of the money going to stuff other than what I intend. Yes, when I can I try to make sure I give to organizations that are 80% or higher but it is hard to find this stuff out.
I don't see any reason why people can't try to raise money and have some fun doing it. Yes, I'm thinking more of the events I reference above than a single person going on holiday but I don't see any intrinsic difference. In my opinion, the important thing is that people are up front about it. If someone says they are going to use x% to support their trip, I may or may not contribute, but I don't have any problem with the idea.