There are no "pay" quests, so what expenditure? Clearing provinces and getting relics from the tournament are something everyone should be doing anyways. The only extra cost I can see is buy 17 KP which shouldn't be very expensive unless they buy a lot of KP regularly.... in which case it's again just asking them to do something they already normally do.
For me there's 2 "costs" that, in my current city, I don't think I want to pay given the rewards.
1. The time-value of scouting/clearing provinces. If I save up 6 scouted provinces, I'm basically delaying a province expansion by a week. Right now, I'm very crunched for space in Orcs. I would rather have that expansion ASAP.
2. I don't have a ton of extra space, and to do this event well, I would need to build a few extra workshops, as well as the non-boosted Tier 1, as well as some Tier 1 residences for the "building upgrade" quests. I could complete the quest without the workshops, but then I'm basically spending a day without supplies, and I'd be foregoing guest race buildings to make room for the level 1 buildings needed.
I could probably still complete the quests without min-maxing on #2, but if I'm going to put in the effort to do an event, I'm going to make sure I complete it. I think I'm in a unique spot, because after Orcs I'm ditching most, if not all, of my culture buildings. So I'd rather spend 2 weeks optimizing Orc progress, as opposed to slowing down a bit for a reward that I'm not that keen on.