I had both the iPhone 7 and 7 plus for a few days and can say that there is absolutely no difference between the primary camera of the 7 plus and that of the 7. If the extra camera of the 7 plus doesn't make a difference to you, including upcoming Portrait mode, then just get the 7.
If the 7 Plus is combining information from both cameras when taking a normal shot, I wasn't able to tell.