Nah, they bring back ok things as they level. They bring back varying degrees of stuff from fish to fish to fish and more fish. Just kidding. Some times these bring back an ink and quill.

As for getting ventures, they're pretty easy to come by after a bit. You can buy 5 at gc for i think 1000 seals, and levequests have em as rewards for certain quests. Treasure maps too can have a dozen or two of them in it.