It's normal to pay for Spotify and Hulu because you get access to stream copyrighted materials monthly for a small fee. It would not be normal to pay for those services just to get a blue checkmark on your profile.
1. For people who post, you will be treated better by the ranking and spam systems. The blue checkmark may be like the “blue bubbles” iMessage thing where it’s not-so-subtly a marker of ingroup status.
2. For readers, you get to see less ads.
I don’t use Twitter much, but I could imagine it being worth it for people who spend a lot of time on the app.