I find it odd that even with a +5 fishing rod, the amount of casts for leveling up once is just the same as if the toon has a basic rod? or just the RNG being a (expletive here). Another toon I have has the "horseshoe" pocket item and it gets really strange stuff - but not the mythical 50-pound salmon. It gets other salmon, though.
I don't think that is possible as the collected fish is used by the cook profession, but usually requires the farmer for other materials (grains, vegs, etc).
I'm not sure if it were ever a hobby in the game, but it's still something people do regularly. I want to say there are a few hidden deeds for pipe-weed though, but I'm not too knowledgeable on that.
It is worthless hobby for me since i have to spend days reaching required level to gather a specific fish for cooking because it requires 130 skill points.