Yeah, thats a tough one. if you are happy with the 18-200 then I would just keep the 105. I’m not a huge fan of Sigma, Tokina etc. but I am a little biased to the main brands Nikon/Canon.
What other lenses do you currently own? The 105 looks like a great lens and the length is great for insects (related to fly fishing). The 105 is not as practical as another lens with extension tubes though and if you are only shooting a minimal amount of macro stuff that might be the way to go.
If you shoot the photos in RAW then you will have more control over exposure and color. Also with a JPG file you lose quality every single time you save the image and also each time you make edits. A RAW file is like a negative and doesn’t lose quality so you can save a file and convert to BW without losing the original.
I use a single handed 9′ 7 weight Sage rod. Its kinda undersized in the winter but I get by. Don’t have the money to have more then the one rod right now