Currently I'm using a 700D (T5i) for a few years and I'm thinking of buying a new body - given current prices of the 6D this might be my only chance of getting into FF.
I do mostly architecture / travel photography (sometimes street photography for which I will still be using my 700D) and my main concern is to improve image quality, even in broad daylight full frame photos seem to be sharper, more clean and rich than from a crop. Apart from selling pictures on microstock sites I'm not a professional, so this means spending significant money, currently I only have the 50 1.8 STM (and 3 EF-S lenses) but I can buy other FF lenses later on. I might as well buy the 80D at about the same price, but I consider photography a serious hobby, and the full frame image quality is the standard I'd like to enter. So would you buy the 6D having only the nifty-fifty lens?
Boiling it down, FF sensors will offer gains in DoF and in lesser noise, especially as ISO increases.
That being said, sensor tech seems to make leaps and bounds and it would also be accurate to say that a new APS-C will perform better than an old FF. Since you're really going with old -> old, I think you'll find that the 6D is an upgrade over your 700D.
That being said, you have to ask, what if I bought newer tech? And now we're back into a conundrum.
Your question is doubly difficult because you've outfit yourself with EF-S lenses - which you'd have to sell secondhand and replace with EF lenses. If you cannot do this right away, and if you spend good time using your other lenses, then I think you will find yourself very unhappy about the decision to move to FF (at least, until you can replace parts of your kit).
Is FF worth it? To me, it absolutely was. Then again, I spend most of my time shooting film and didn't have to sell off my lenses to get a FF (I also chose to buy a 5Dmk2 - considerably old by today's standard).
Will it be worth it to you? Personally, I think you need to look really hard at those gains and decide. If your main goal is the nebulous "Image Quality" then I think that you should not make this decision - as it could be other factors about your shooting that would help you improve your IQ...like lighting, technique, lens choice, etc.
Generally speaking - until you can accurately and finitely describe a problem that is a show stopper in your current gear, and that is only solved with a new camera/lens/whatever...then you are not actually going to find the upgrade beneficial to your photography.