You probably don't "need" it, but if you are curious, I suggest you get the Mini. Heck, I would recommend it anyways, cause it's awesome! I bet you'll use it as your primary device at home.
My iPhone is for when I'm out and about.
My Mac is for work, emails video and photo editing, file storing, music andmedia management and when having to do intensive online tasks (online trainings, web forms, etc.) . (Obviously surfing the web and fun stuff too)
My iPad mini is for when I'm home.. relaxing.. Surfing the web, shopping, social networking, HBO Go on the couch, reading, quick emails, you name it!