I think you would benefit moving from the cropped sensor to any of the full frame sensors.
You need to go and put your hands on the cameras and see how they feel to you, weight, size, ect. The way the camera handles to you is more important than any review or technical rating.
If you have a FF sensor you can buy equivalent FF lenses vs the cropped lenses, so our next upgrade you can keep the lenses and sell the body.
On the wi-fi issue - i think its a hand feature when traveling. Neither body i have has it, my point and shoot does. Sometimes when i travel , i only have an iPad and its nice to link the point and shoot up and send pictures to family
I don't think the 6d has a pop up flash, so you will also need a flash. I have the 270 and 600, i would recommend the 270, its easy to carry and does what you need for most flash situations i have.
Keep in mind the weight and size of your kit- in my opinion , lighter and less is better,especially when you travel.
hope this helps!