> I have every right to invent a device which allows me to create an artificial wormhole which then allows me to remotely observe this party (see the Arthur C. Clarke book "Light of Other Days"). The partygoers will have no idea I'm observing them and since they wouldn't sell me a ticket anyway, they won't see a difference in their revenues.
Voyeurism may or may not be a crime in your jurisdiction.
That really depends on the exact laws and how they're worded, and what kind of party this is. A party which involves ticket sales (as was stipulated before) is not a private house party, this is the kind of party that happens at a club and is something that's "open to the general public" (just like a concert or movie), so I don't think voyeurism laws would apply here. There's no expectation of privacy in a setting like this; anyone is allowed to enter, as long as they pay the ticket price and don't exceed the venue's capacity. So if you come up with a way of looking inside the place, getting the viewing experience everyone else has there, without trespassing in any way or interfering with other people there, I don't see how it could be a crime unless they invent a new law to address it.
Here's another thought experiment, but using modern tech: suppose there's a party like this (open to the public, tickets required to enter), and there's no rules at the club forbidding cameras or communication devices. If you pay the ticket price, you're allowed to enter and take photos all you want as long as you don't disturb people and make a nuisance of yourself. (I'm pretty sure any normal bar or club these days is just like this; people take photos of themselves at bars all the time.)
You don't want to pay the ticket price to get in, but you want to see what's going on there. Your friend however wants to go in, so he buys a ticket and enters. While inside, he whips out his phone, and activates an app which contacts your phone, and then streams live video from his phone's camera to your phone. You're now able to see and hear what's going on in the party without buying a ticket, apparently legally. Fast-forward a few years and instead of watching your buddy's video stream on your 5" phone screen, you're watching it on a VR headset, so it's almost like being there. My wormhole idea isn't much different from this; it just doesn't require a confederate.
Voyeurism may or may not be a crime in your jurisdiction.