I like wild collecting the wood as well. I don't always find something much I like, but sometimes you do find something great looking. Plus, it's nice to just get out and poke around.
If you are collecting from salt water, soak it for a while with several changes of water to leach out as much of the salt as possible. (will also help with the initial tannins, and water logging).
I wouldn't put punkwood in the tank, but I won't pass up a piece of softwood that I like. Just realize that you may have to replace it after a year or two (or longer, depending on the size of it).