Ok, first id like to say that im fairly new to gems of war but i have a few suggestions to improve this already great game. There will be a couple thats probably been brought up countless times. That said, here are my thoughts… First the easy things, pet gnomes included on explore battles. Get rid of the minor traitstones on gnomes and with vault keys. Include an option on treasure hunts before it starts to use 1, 10,50, 100 or 1000 treasure maps, then multiply the winnings the selected amount. On the guild tasks, you should receive better rewards the higher the levels. And the legendary tasks should at the very least give 1 legendary troop each time. A couple keys and maybe some glory is an absolute insult for 1 million gold! Maybe every 3 months have a gnome week event in place of that months gnome weekend. Some players work on weekends and miss out on that special event. So those were the easy fixes, here are two ideas i would love to see on this game, especially this first one. For every troop in the game, put a reasonable gold value on them, then create a marketplace to sell your extra troops. Charge a small amount of gold to list your extra troop then post it to the marketplace. Have it be a list of all the troops everyone is selling. Include a search bar for those looking for a specific troop and an option to refresh the marketplace list. If someone chooses to disenchant their extra troops, there should be an option to only disenchant the ultra rares and below. Disenchanting legendary and for some, mythics for a few souls is insane. There needs to be a way to trade and sell extra sought after troops. And finally an idea for a new event or mini game like the treasure hunts. Maybe have it similar to guild wars, where every day you need to match a certain coloor as many times as you can, with better prizes for more gems matched. The opponents get tougher as you go, so there are better chances to match more gems. Thats all for now. If anyone wants to expand on these or add your feedback to this post, please do it! The more traffic this gets, maybe theyll be more likely to consider these or other improvements.
Had to make that more readable. May comment later.
The devs have already said no to the idea of using multiple treasure maps at once to get increased prizes. They do have a treasure map revamp on their roadmap. They haven’t shared any details yet.
They’ve also said they’d never add troop trading or marketplaces. You basically can have as many alts as you like in this game, so that pretty much hinders those mechanics.
Currently, they have said no to pet gnomes in explore. They want to make sure people still have an incentive to play PVP. However, they did say they may re-evaluate this one in the far future.
As to your point about legendary tasks, many of us share your pain. There are a gazillion threads on this topic. The devs don’t agree though. Basically, their reasoning is that for that million, you are paying for those resources for 30 people not just 1 person. 
As for your new event idea, I like the concept. I always keep my fingers crossed for new minigames.