Regarding only 20 ribbons in the bonus round, while this might seem stingy and unfair you need to understand the reason behind doing this.
The objective of the bonus round is not for you to make significant advances, it is to allow you an opportunity to continue playing the event.
While I hate this event as much as the next player I do understand what Inno has done and why they are doing it.
Believe it or not it is based on your feedback.
A year ago events had a fixed quest list and a limited number of quests. The chances of evolving even a single building was marginal depending upon how much bonus currency you received in the chests. Sometimes you could make it, sometime not, depending on your luck. Players complained that it was not guaranteed to get fully evolved even if you completed all of the quests.
Also many players could complete the event too early. I myself usually finished the event in 1/4 of the time because I planned well. We would usually turn it into a race to see who could finish first.
To give those that finished too early a chance to play longer or to give you that extra edge to get that final evolve the solution was to add the more difficult infinite quest line.
One drawback however with "infinite quest line" was that really determined players could obtain more prizes than was originally expected by the developers.
The fix for that is to reduce the event currency in the infinite quest line. This provides players that really want to play the event longer or those that are almost at their 9th or 10th evolve an ability to be challenged by the event while at the same time not making it overly easy to get too many prizes.
As an added benefit, if you want to pay real $$$ for an advantage you have that option as well.
Remember, the alternative was an event with a limited number of quests and when they are done, they are done.
I think people were still surprised that it dropped all the way to 20 from 57, since the official intro for the event only said the amount for the bonus quests would be reduced. Fortunately, we knew in advance it would drop down to 20 because of Beta and the info being on Elven Gems, or at least those of us who knew where to look, knew this in advance.
As for fixed list versus infinite, you may notice the most noisy about this are the ones who want to go back to the set, limited list, so that they can do them all in two or three days and then not deal with the event until their preferred daily prize shows up.
One other note on this event and the transition from normal to bonus quests, from what I experienced, and others have posted about, I think the devs miscalculated the point this transition should happen, rather than doing it on purpose. If they wanted players to max the building at the end of the normal quests, they were off by a couple of grand prizes. I, and others, finished the normal quests still needing between one and three more grand prizes to get that 9th artifact, depending on our luck with bricks and extra ribbons from the presents. So almost everyone wanting to max the building has had to do a bunch of the bonus quests for those 20 ribbons each. That part has not been fun at all. Sure, instead of doing the bonus quests, we could have sat around and waited for the next FA, which will almost definitely have Gingerbread artifacts as prizes, but we are an impatient bunch of players and want to max the building now, not later. lol
Oh, and it has been way less than a year since the last event that had a limited list of quests. The last one like that was the Easter/Phoenix event. They made that list so easy, and not rewarding enough, that they added that extra batch of quests part way through the event. After that was when they decided we needed an infinite quest list that also had to be randomized, so that people would never again be finished in just a couple of days.