First off - I’m NOT complaining about the frequency of rare/uncommon/common quests, so the 4 or 5 of you that attack everyone that has a complaint can save it this time.
So - are the common quests worth it for players of any level? Peronally, the only common quests I ever do are the finding recruits one, and only if the timing is such that I’m low at that point. The crafting item and battle item ones seem like way too little reward for banners spent. When I do the math for the gaining experience one, it always seems like a better idea to just farm the world map. For uncommon, again I do the recruits one and sometimes the experience points if I am close to leveling up. I suppose it depends on if it’s a 3/4/8 banner or 6/10/12 banner setup (which both happen at the common level). It seems to me that the variation between common and rare quests is way too large. The common ones are mostly useless, and the rare ones are amazing. If they would bump up the common rewards and decrease the rare rewards (while tweaking the frequency rates) I would probably do a lot more quests. I would even consider them a welcome diversion from farming the same boring levels over and over and spend more flags for a bit more variation.
EDIT - I can see how the one that gives you gems would be valuable to someone that spends no money at all to buy gems. They cost a ton of banners, but if you need the gems it only costs you time.