In my opinion star master and lucky thief already provide a good amount of help, even though the rewards are random. In addition, the items needed by a player can vary aswell. For myself I can say that at the moment I have tons of blue eyes in my pocket but no mushrooms or purple powder. And since I cannot sell blue eyes for GXP, I have absolutely no use for them and would always prefer another item.
Also I think that rare items should stay 'rare' because that is the whole point, isn't it? There is a reason for blue eyes and mushrooms to be more expensive than leaves or powder. It makes a maxed out throne so much more worth.
Anyway, I agree that upgrading the Forseer consumes an insane amount of mushrooms and eyes, so I would like to suggest another change:
Now the chances for magic items after completing a ritual are 35%, 35%, 20% and 10%. (I don't know if the numbers are correct, but it surely is something in that proportion.)
What I would like to see is that these chances scale to the size of the outcome gem from your ritual. In numbers that would mean e.g.:
Starting at the current chances for a gem worth < 3k up to 20%, 20%, 40%, 20% for a ritual resulting in a 999,999 gem.
A size of more than 1,000,000 would remove leaves and powder from the spinner and just provide a chance of 66,6% for mushrooms and 33,3% for eyes.
I think this would be not just one more way to encourage big rituals, but also making players 'earn' these magic items and not just randomly throw them into their pocket.
(Btw I do not know why this topic is in 'Troubles & Solutions', maybe this would rather fit into 'Ideas for shaping KoT'.)