I think you hit the nail on the head. I think a DLC with only attractions and such things could work. But it needs to introduce some fun mechanics and not just be mostly cosmetic like the cinema/bowling alley/etc
Perhaps something like a river cruise and working pedestrian bridges could work for a DLC. Or maybe also raised paths and catwalks in the aviaries.
I would have also mentioned the Viewing Log and the Domes as they are just variants of the basic Viewing Gallery, the Viewing Stands as well. Yeah, its nice to have them, but its just a different building with a few camera view points no different than what we already have. They simply don't do anything of interest even the Zip-line is more unique than them and I am a particular critic of the lacking interactivity of it. Like what is the point of all of these attractions, really?
Frankly, I can barely tell a difference in what the attractions do to attract guests. I know they each have some sort of indication as to a Guest Type (on paper), but does it really amount to anything? The way the game is setup the guest management is hobbled, we can't even set admission prices which takes away our most fundamental ability to control the performance of our parks. What's the difference between an Adventure or a Luxury Guest? The modules you set in the amenities? The game doesn't give good feedback its doing anything differently based on the label attached to it.
Worse, attractions have no interaction with the animals, so they don't really feel like they are tangibly there. Even the tour gets this right by letting the animals attack the vehicles. A gallery or dome can't be effected by an animal's behavior at all. I recall a phrase some like: "A shark in a tank versus the open ocean is seismically different" or something to that effect and its true. We have a virtual zoo/aquarium which is fine to see in person, but in a game I do expect to actually have something to do. JWE2 isn't exactly a good movie either, so I can't just passively watch and enjoy it for that long otherwise you notice the limited animation sets and lack of behavior from the animals. We need things to feel more like a game.
Why can't a mad Triceratops ram a viewing gallery? Why can't I set admission fees? Why don't the Guest Types mean anything in practice? Why are the attractions just static reskinned buildings with camera views?
I know I am rambling a bit now, but its a bit frustrating how 1-2 months after every single DLC we are back on here asking ourselves the same couple of questions. Making more demands for species and decorations since we are bored of what we have and only new content seems to fill the void. Then we try to analyze the game and wonder why more people aren't playing and sticking with it after a DLC drop ignoring we are just seeing cosmetic changes and throwing a few Sandbox toggles and quality of life fixes in there. JWE2 like its predecessor is lacking compelling gameplay to keep the player coming back. The systems are too shallow, too few, and it feels mostly like annoying busywork and that is probably what the general audience sees if they play a month or two and realize it.
As for the river cruise specifically, we are overdue for a water-based attraction. Not only is it visually much more unique, it has baked in movement making it more interesting like the Zip-line as there is something dynamic happening. I think for the intersections with paths and regular tours you could auto-generate overpass bridges. I have a thread about some attraction ideas I had. Most of my in-depth threads are interconnected, so just keep that in mind if you want to go down that rabbit hole.
Reference: Guest Attractions