The reward is poor in every age - in bronze even, it takes too much space...
And really - if someone is so desperate about 5% boost for coins and supply - why don't you rethink your city, because it obviously isn't efficient and no 5% boost will improve it, seriously, it will only take so much space you need for production buildings to make it more efficient...
Quest 12: Mahātmā Gandhi: "Research a technology
OR donate 300 goods either from your current era or the previous era to the guild treasury" and "Spend 10 Forge Points"
It is impossible again for bronze age, if you don't want to move to iron age. I donated 300 goods from the following (iron age), but it doesn't work. All technologies are already researched of course.
It is the same like in fall event quest line 1:
Quest 10: Greva Darn: "Research a technology
OR donate 300 goods from your age or the previous to treasury" and "Spend 7 Forge Points"
I know that era-potatoes like me are not the target group for these events - never the less: what a pity to miss this beautifull designed Building again.
Kind Regards