You raise two issues so allow me to share two responses:
First, why do few companies, upon receiving your unsubscribe request, ask you why you unsubscribed? I don't refer to the opt-in box to write your reason on a web page but a manual and personal email message from marketer to you. It rarely happens and it should if the company is sincere in hellos and not goodbyes.
Second, the easiest way to determine the valuable tweets is to search for retweets. There are websites set up for this purpose, tracking the frequency of retweets. If your tweets are categorized five ways and only two ways are retweeted, perhaps you should nix the other three ways because that would be the noise.