So, I've just got the 6+ and, suddenly, my Mini (2, retina) doesn't make as much sense as it used to. Anyone else in a similar position and wondering whether to jump to a full-sized Air 2?
Of course, most wanting the iPhone 6 have debated on which one to buy, and if the Plus is chosen then wondered about the need for an iPad, especially a Mini - next week, wife & I will purchase iPhones 6 and after looking and handling these newest Apple models have decided on the regular size phone - I'll continue to use my iPad 2 for reading, games, photos, and light web browsing - I would not do most of that on an iPhone 6+; my wife will likely not change her habits when using her Mini.
My suggestion is to list the activities you do on the Mini now (maybe the top 10 or so), then perform them on the iPhone 6+ - if you are happy doing most of these activities on your new phone, then the Mini may not be needed; however, if you still prefer the Mini for many of your uses on that device, then keep both - about the best that I can offer - good luck! Dave