I didn't finish the event, so I can't say too much about what I thought about the overall effect, but from what I have observed my thoughts run along these lines:
1-The pay quests are an interesting idea, but only if the rewards are worth the effort. In every game I've ever played, reward vs. effort is a huge factor in whether or not I enjoy it. I don't mind a bit of grinding; IF the rewards are worth my pain. (I play RPGs, I know what grinding is) Not only were the amount of goods required ridiculously high, but the rewards were small. Asking for so many goods that even a high end player has a hard time coming up with, in exchange for a few beets to gamble on a
chance to gain a prize that isn't much better than the current chapter's buildings, is not balanced.
2-There needs to be more variety to the tasks. Endless loops of PoP spells and gaining relics is getting old. I don't need any more PoP spells, I'm trying to pump out the Magical Manufacturing spells to use on my factories to get more goods to help out my fellowships. I don't think it would take away the challenge to be more general with certain things, like "gain a spell" instead of specifying PoP spells. I also agree that the quests should encourage fellowship interaction and have the option for neighbor interactions, as not everyone is in a fellowship. Generalizing the solve encounter quests so that the tournaments will work will probably help encourage participation, and give those who've over-scouted another option. And for those are over-scouted AND have all their buildings at max, having the option of scouting or upgrading a building still means they're pretty screwed. And I really don't think having quests that require tier three goods is a good idea. Not every fellowship has bigger players who are able to give the smaller players lopsided cross tier trades for those goods, especially if they're broke from the event too.
3-We need more buildings that give you different things according to what chapter you are in. The orc nests were great. It gives the lower chapters a nice amount of supplies and everyone else orcs. We also really need buildings that give mana to those in wood elves and beyond, and buildings that give other things needed for the higher chapters.
4-I like the "decline a quest" idea. Sometime you gotta skip a question on a test to finish the rest, and I think the same holds true for the quests. (And no, I did intentionally rhyme that) Maybe give them the option of coming back around to it later if need be, but let them do what they can before the event is over. Not everyone has time to do all the quests, but still may want to participate and do what they can.
5-I'd really like to see a reward for finishing all of the quests. Personally, I get bummed that there isn't anything special at the end of the event. Especially since the rest of the rewards are gambles. I'd like to see rewards for finishing all of the quests in each line, and maybe even a small prize for those who participated, but couldn't finish. Maybe a couple of things to choose from so everybody could have an element of choice and pick what suits their playstyle best. You could have different prizes to choose from depending on how many quests were completed, so if you managed to finish them all you get the pick of litter.
6-The buildings should be worth the effort. While I understand you don't want overpowered buildings, from a player's perspective, if the rewards are on par with the buildings from my current chapter, I'd rather spend my time and resources building my regular stuff instead of slowing down my city for sub-par rewards.
On a positive note, I'm glad we didn't have to click any kind of confirm button when we collected beets.
I'll edit and add more later if I think of something.