I have had a thought about a slightly different kind of adventure, to spice things up a bit.
How about an adventure, where you proceed like any other current one, but on defeating the last leader camp, you uncover a random resource that could range from a wheatfield/farm, a stone mine, a copper mine, all the way up to something more exotic, like gold/granite/titanium mines, or an e/w sawmill with a finite set of resources, there could even be an almost mythical gem pit island , for the extremely lucky.
My idea would work something like this, once you've conquered this island, for a set time of say 28 days, this resource would deliver to your stores once a day, and at the end of the period would run out of the resource.
You could only have one working currently at a time, so you would have to wait for the 'fish island' to exhaust its stock, before you could attempt a new adventure, and hopefully a more desirable resource.