Running 360 degree sound isn't cost effective and it doing it the cheap way makes the venue sound like crap. Also no one over 18 wants to dance with or have anything to do with a bunch of 16 year olds in a club setting, 16 year olds will pay cover and buy nothing else. 18+ ensures people will come inside the venue. The spring chickens will attract the 21+ males, who will empty their wallets in an attempt to look cool and attract the chick.
Creating an adult only venue, completely isolated separate from the rest of the event would be the best option, period. Include access to the club portion as part of season pass sales, free access to "Club w/e" every night of HOS with purchase of season pass. Discount for current season pass holders. Sell 18+ and 21+ VIP packages. Put a few cabanas back there. Open the cabanas at 4pm. Have the DJ play for the VIP's. Bill it as having a "Private DJ" etc, exclusive Lounge area and VIP booth, include a couple of drinks with the 21+ one. Access to VIP pre-party. Include a VIP buffet. All these things would cost minuscule amounts for the park to set up. Considering that the typical VIP booth in this area goes from $300-$500 for a nice place to sit and have people look at you at clubs in the area and on the strip, the park would be able to beat that price point easily and turn a profit off the sales from these areas with extreme ease, with the proper marketing effort.
One or two bookings at $100 should pay for the whole VIP thing. Include a group up to 6. Include a one time use HOS Quick Queue for each of the mazes for each of the guest. That's free for the park to issue, but added value for the consumer. Use a one time use QQ to get the party back to the club area and drinking and purchasing stuff. If at first it doesn't get filled offer the package for a discounted rate in park. If not after 30 minutes, give it away as a "prize"... Get people talking about it.
Include extended packages that include tours etc and bump the price up accordingly. As the packages get more popular bump up the price. Selling two or three of these packages should be able to to cover operational cost for a night. That's not even including cash from cover or from the bar... Which, my suggestion would be to sell the cocktails from all around the park in one place, As well as a few exclusive drinks you can only find in the bar you have to pay cover for... People would pay the cover just for the convenience of not having to walk around the park to experience all the drink offerings. Not to mention, you get the added value of keeping the rest of the park clean because most of the annoying drunk guest would be attracted to the bar.
The club could be collection of all of the themes of HOS. Pirate, Vampire and nurse servers. Host is a random ghoul, so is the DJ. Go-Go's can be w/e. I'd suggest the name and theme to be something like "Club Purgatory".
A couple of unused scanners the park has laying around. Maybe a few laser rentals and a tent rental. Inside of the tent should be black. 1 fog machine set to manual control with only the stage manager and tech authorized to touch it. Dressing for the bar area. Costumes, Serving supplies...
I can imagine the whole thing should be able to be executed for well under $20,000. Tent + Lighting would probably be the most expensive things. The area would only need to generate $3,000 a weekend roughly to pay for itself. It's operational cost per night would be amount to 8 hours per day for 5 servers/bartenders and 4 entertainers. At a median wage per hour of $10 that's $720 to operate nightly. I'm not including cost of security or Stage managers or Technicians.
Either way, that means it would need to turn just over $5,000 a week to turn profit by the end of the event with a fairly inflated budget, (I think it can be done for under $10,000) counting on the re-use of in-house assets.
Lets say less than 1% of the park's visitors for an at capacity day visit on average. Admission is $5 bucks for 21+. Let's say 100 21+ guest a night chose to enter. $500. Let's say 18+ is $10. Let's say 200 choose to enter. $2000
Of those 100 guest, 50 buy a single drink at $10 for the whole 5 hours the event will be open to everyone(6 on saturdays). $500
Let's say on average, the park sells 3 VIP area things at a median of $150 a night. $450
The grand total is $3,450. That's per night.
Using a fairly low margin of return and low estimates, the idea is viable. If it can do roughly what it should be able to do in one day each week, It should more than pay for itself, and mind you, these are some pretty abysmal, low-ball estimates. I can imagine many, many guest will gladly fork over $5 bucks if the experience is much talked about, and again the clubs here suck. I can imagine at least 200 drink sales a night on the low end. It shouldn't be that hard to convince your peninsula season pass holders to go to your park instead of driving down to va beach. It takes twice as long to get to there.