If you want to talk about the HFS in game terms, the HFS was always meant to be a game over. (I would say it's a punishment for being too greedy, but that implies that you're going against the intended design or you're meant to learn a lesson because of it, and this is supposed to be how your fort ends.) The original, 2d version of the game would just instantly kill all your dwarves if you pulled too much cotton candy. This was because the original conceit of the game was for you to make your own fort, have it mysteriously be destroyed, then make an adventurer and explore its ruins. This is largely why there is that tagline "Losing is Fun", the fortress is supposed to crumble to outside invasions (as opposed to the real killer of forts, FPS decay and/or deciding to play something else for a while).
Adventurer mode was ignored for many, many years, though, fortress mode was basically seen as the Dwarf Fortress, and players didn't like arbitrary game overs, so with 3d came the ability to have a chance to survive, although you were still meant to die.
Getting stupid amounts of meat isn't a deliberate reward, it's just the procedurally-generated consequence of Toady having made it fairly likely that a decent proportion of clowns are made of meat, and meat is edible in DF. This happens to be something you can benefit from, but it wasn't an intentional consequence, as you were never intended to win at all. I'm sure if there was a deliberate reward, it would be more like gaining slabs from defeating the guardians of vaults. I mean, the more tangible reward for defeating the HFS is being able to suck up all the rest of the cotton candy in relative peace.
Likewise, consider that the HFS is made of a material you cannot use in any way other than digging unless you're using a bug (which itself implies the "you aren't supposed to use this"). The HFS is pretty specifically designed to be as unrewarding as possible to underline the pseudo-punishment nature of it.
That said, if I'm recalling the older versions of DF for you whippersnappers that were knee-high to a grasshopper back in the golden days of less features and more game-breaking bugs, there were three kinds, and each had their own little quirks to their big top. Hoppy clowns had swamps in their circus ring, with swamp vermin like turtles and blood gnats. Wiggly clowns had "yellow filth" and "brown filth" (yes, that's biological waste in DF), engravings of "depraved acts", and lots of prisoners to apply their "corrupt intentions" (which some dwarves admire) towards. Fire-eaters have magma pools, ashes, and charcoal.
This all, at the least, implies the intention to have some sort of unique flavor to each of the clowns and have their particular rings of the circus reflect them, but it probably proved too much effort when Toady went and added in procedural clowns with Mr. Potatohead parts. The swamps in the HFS that have evil biome vermin are probably the most interesting (you know, once you get "corrupt intentions" out of your system), as it definitely implies that normal life like turtles can at least hypothetically live in the HFS (provided they aren't being spawned infinitely just to die horrible deaths being swallowed alive for fun), and it's more like a super-evil biome. It definitely supports the claim that not everything in the HFS needs to be poisonous, at least.