Currently- Indigo caps are so underutilized and undervalued and require so much per*exp to even start seeing... And in their current numbers are not worth scouring large cave systems to maybe come back with all of 3 caps after an hour.
Most people have no idea what effects they even do in recipes- To the point where even the "not-quite-official-but-still-often-used" hafen cookbook doesn't even list them as an ingredient. All I've discovered personally is they affect perception when used for autumn steak maybe? But that's besides the point.
They are currently so rare and so awkward to utilize that no one even cares about them, so we have no idea even if there -is- a value to be had with them. I mean you even allow troll mushrooms to be planted- Which immediately throws out the argument of intentional rarity/skill gating as a reason not to.
Either allow us to plant them in a garden pot, or keep the "high tier foragable" Theme of them intact and increase their spawn rates and quality range by a very generous blip. As even when I can find them- They are almost always in the low 10s QL wise.