Probably doesn't really matter. If you get a second body that is less functional that the one you currently have,
you'll probably never use it. If the second body has more function, then that will become your primary camera and your current body will become "backup". Either way, the second body is mostly more of a pain in the .... to carry,
handle and use unless you have a competent "assistant".
have you tried it? it sounds like you are guessing. there are plenty of bags and harnesses which allow for relative convenience in carrying two bodies and two lenses.
when I shoot football, I would really like to be able to go from a Tele zoom to a wide angle between plays. it isn't worth 3500 to me, but it would be more convenient.
In a nutshell (No more Squirrels Please), jdramirez has it, it's convenience to have a 2nd Body, unless your a Pro, then it's a must have. It get's down to how much convenience/how much your willing to spend.
I shoot various types of Images, but my main interest is Wildlife, I absolutely need 3 Bodies at all times connected to 3 Lenses when on Safari, 70-200/300/600, the 300 will depending on conditions be either the 300 or the 400, but will now be the 200-400.
It's about speed and not wanting to waste time changing Lenses, and it's about not wanting the Sensors to be covered in Dust/Snow/Water etc. The only downside is weight, but currently I have a Sherpa, more commonly known as a Son, so when we Travel, he obligingly helps me carry the Gear, in fact, this is the largest cost of all, Children.
So depending on what you shoot, a 2nd Body is to me, totally necessary. Fortunately today we are spoiled by choice at all Budget Levels, I use 2 x 1Dx & 2 x 5DMK III Bodies, but you can just as easily go for a Pair of 6D, or a 5DMK II & a 60D, work out what your needs are, what you can afford, try the various combinations, make a decision, go have Fun.