Only way to get exp on a steady basis is adventures (steady basis, as in, not 1 time quests).
There should be some alternatives to get exp. Some ideas..
1) Daily quest rewards the normal loot + exp
2) Getting all collectables on the island rewards exp instead of nothing.
3) Resource exchange tab in the Provision House. X amount of Y item = Z exp
4) Repeatable quests for doing different actions
4a) Use 50 Aunt Irma Baskets on friends.
4b) Build 1000 troops
These are just some thoughts.. And please keep comments positive. If you have ideas yourself, please add them. If you disagree with some of my suggestions (or one by another person), please articulate as to why you disagree rather than saying something along the lines of "That's a stupid idea".
Thank you and Merry Christmas everyone