Thanks for the responses.
I am not very familiar with sandbox games, although I am in favour of games that let the player express their own creativity (Minecraft and Captain Forever spring to mind).
I'm also fascinated how simple rules can produce unforeseen consequences, emergent phenomena. (Game creators do not always know the optimal strategies. It may take years for the players to discover them.)
I can certainly set some of my own placement goals. Thanks for the suggestion! I would like to balance optimal positioning along with redundancy, so the hive is not too fragile to attack. (So far I have managed to withstand all bear and wasp attacks, so I don't actually know what an attack looks like. So I think absorbing and surviving an attack should be one of my goals! Yay!)
I certainly wouldn't want to eat away at the sandbox style of the game. I was wondering if there might be a best-of-both worlds, so a player could choose whether to set their own goals, or achieve those suggested by the game. But perhaps the existence of one option negates the other.
On Freenode IRC you gave me some nice suggestions:
"What's the fastest you can get 600 jelly from scratch? What's the smallest population hive you can get 600 jelly with? Can you get 600 jelly without researching a jelly refinery? Can you get 600 jelly without upgrading anything but the Workshop?"
These are interesting ideas which I hadn't considered. Perhaps some suggestions like this could appear in the game, even if they aren't explicitly coded as challenges, as a starting point for people like me who never imagined setting their own goals.
I'll go back to the game with this new point of view (and --verbose) and see how I get on. Cheers!