Why do they need a "nice venue"? Why wouldn't any airport hotel's conference room be sufficient? They wanted something nice, more than utilitarian. They wanted luxury, and how does an "effective altruist" defend that? Because luxury makes them "more effective" of course.
If someone is spending lavishly on pitching to me[1], I start to really question the deal. At best, they're showing me that they don't mind wasting money on things that don't matter. If you want to impress me, wine and dine me by taking me to McDonald's.
[1] I have been picked up in expensive sports cars, I have been taken out to eye-wateringly expensive restaurants, etc. This is the sort of thing that raises big red flags to me.