Well, you'd really need to evaluate your usage to see if you can fit one into your life. For some reason, I've always tried justifying getting rid of an iPad for a 6 Plus, but that just leaves me with a large phone, not a tablet. The iPad is a good media consumption device, but it's also a great work tool. If you're happy with your phone for web browsing and video watching, an iPad may have little to offer, but I could never go phone-only because of battery life. If you're going to be out all day, you can't game on your phone, stream hours of video, etc or you run of juice long before you get home and I don't want that battery anxiety.
I use my iPad as a gaming device, both casual and intensive. I use it as an email device, web browser, email client, drawing pad, and as a tool for studying and research. My biggest justification is using the iPad for documents. I read thousands of pages of research papers, class notes, journal articles, etc. on my iPad. I can keep these pages in one compact device. It's natural like a piece of paper and allows me to annotate, search, and jump between them far easier than printing them all out and keeping them in 4" binders. I am teaching a lot right now in grad school. I work the problems (accounting) by hand, scan the pages, and then highlight and add notes to them. I teach by referencing my iPad instead of trying to juggle a textbook, binder, flimsy paper, and a marker. Everything I do on my iPad, I
could do on the Plus, but the larger screen of the iPad makes it nicer. Really, the convenience of one device is really the only benefit to consolidating. The Plus is pretty much a compromise in every way when compared to an iPad, but it's a really fund device.
Also, society views a tablet different than a smartphone. Like I said, I often toy with the idea of using a Plus in place of an iPad, but I can't teach from an iPhone or take notes on an iPhone, it's just not professional. Many professors forbade the use of phones, but didn't care less about tablets.
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Still, if none of those things apply to you, a Plus may be sufficient. You can buy an iPad and give it a week or two and see how you enjoy it; that's how I realized I didn't care for the Mini. If I didn't have a work-related use for it...I might be content having just an iPhone and a rMB, but it's e-reader/document annotator abilities are just too good to be ignored...man I sound boring!