First of all, players don't "use" moves. A move is something that player character's actions might trigger, but the trigger itself is at the GM's discretion. If you don't see any decent possible consequences, don't call for the Spout Lore move. Just give players the information they asked for, preferably making a GM move in the process. See also How to ask nicely in Dungeon World
Give a tip and make a soft move
Let's say you've asked them to roll +INT. 7–9 result is a partial success. You can give a tip, like "something about this might be useful", without any specific details. That's how it is done in the SRD example:
GM: Heh, yep. You’re in a murky pit, and there’s a shadowy humanoid shape, mottled and eyeless, moving towards you, mumbling.
Fenfaril: Mumbling shape, huh? What is that thing? Is it going to attack me? I’m sure I’ve read about them somewhere before, maybe at school?
GM: Could be. Spout lore!
Fenfaril: Bestow your knowledge upon me, brain. I rolled an 8.
GM: Well, of course you know of these things—the name escapes you but you definitely remember a drawing of a creature like this. It was in a hallway, standing guard over something. You know there’s a trick to get it to let you pass but you can’t quite remember.
However, the revealed fact doesn't have to be potentially useful. It's on the player how to make it useful, not the GM. If you want to tell "something that is interesting but for which there is not a painfully obvious way it is useful" — find an interesting fact, which is completely irrelevant in the current situation. A player still might invent a creative way to make this information useful, sooner or later:
— A few goblins were hiding in the woods. They open fire — several arrows are flying towards you.
— Goblins... I'm sure I've read about them. What is their greatest fear?
— Spout lore. Roll +INT!
— It's 9.
— Well, you've read a book titled "Beast Masters and Slave Drivers" by a prominent goblinologist. You remember that a goblin tribe is organized in a four-tiered caste system made up of lashers, hunters, gatherers, and pariahs. The status of every family in the tribe is based on its importance to the tribe's survival.
Lastly, a partial success is the "yes, but" kind of result — you can give information and also make a soft GM move. "Reveal an unwelcome truth" suits the narrative quite often. The goblins' example:
— Spout lore. Roll +INT!
— It's 9.
— Well, you remember that goblins seek to trap and enslave any creatures they
encounter, but they flee from opposition that seems too daunting. They attacked you, that means their numbers are overwhelming, and they will probably try to capture you alive.
On 6- you don't have to give any information at all. Just make sure something bad happens.
The rulebook says:
On a miss the GM’s move will often involve the time you take thinking.
As a GM, you are free to make any GM move, even a hard one, not only "reveal an unwelcome truth". In the goblins' arrows example a miss could mean the arrows finally reached the PC, while he/she were still trying to remember something interesting or useful about goblins.
Your "failed" option didn't look like a miss
If they were to have failed I would have said:
Unlike other areas, Oostar is not as progressive on the rights of nature creatures. Sentient mushrooms are considered a delicacy here.
Well, that looks like a success to me, at least a partial one. "Sentient mushrooms are considered a delicacy here" is definitely a useful piece of information, considering the fact one of the party members is an anthropomorphic mushroom.
Yes, you are foreshadowing troubles with this answer, but it complies with the "Fill the characters’ lives with adventure" GM agenda quite well, specifically with the "Think dangerous" principle. "You successfully bought all the ingredients and made a delicious meal, nobody was hurt in the process, everyone's happy" scenario isn't very Dungeon World-ish :)