In some of my Live cities, I won't finish the Winter Event (all 71 quests), yet I've got complete Winter Spires. It makes no sense to me to complete an event, yet not have the completed main reward.
I think I had re-entered the game right after the winter event had started and only completed a few quests on beta and gotten enough for a level 3 Winter Spire. However, it was decent as the art didn't show any scafolding and it is of use.
Still, Inno pulls the hype of telling everyone that it would be possible to get a full Colossus without spending diamonds, and yet we have folks who were on for each day of the event, collecting their free daily footballs, completing all quests (including getting 2k footballs as a reward for doing 30 quests), and were given some footballs as part of the re-balancing bit that they only wind up with a level 8 or 9 prize in the end (and falling off the ranks).
That's the bit that really got me. If everyone was promised something in the end then that promise should be delivered; especially, when they (the players) were working hard to complete everything and gave it their all.