Is it worth upgrading to the Canon 6d from the 70d?

That upgrade would be an utterly pointless waste of money.

The vital piece of missing information in your question is what lenses you are using. If you have the normal kit lens supplied with the 70D (18-55 or 18-135) then spend some money on an upgrade.

Go for an EF 17-40mm f/4 L, a 50mm f/1.4 and a 70-200 f/4 IS L.

They will improve the quality of your images WAY beyond a body upgrade.

Canon 6d Upgrade

I'm a tech nut, always playing with new gear just to see how good it is, I shoot with a couple of Nikons (crop sensor) and that's pretty much all I need, I don't often need huge poster sized prints and I'm experienced enough to compose the shot I'm looking for pretty much at the time of taking the snap so I don't need to do much cropping.

Only reason I'm considering full-frame is because I'm happy with the quality I'm already getting, I couldn't really ask for anything more, and rather than upgrade my D7000 and D7100 with whatever they replace it with, I'm thinking about stepping up to the D750 it's a logical step for me and it makes sense.

Any improvement in quality is a bonus, I'm already a satisfied customer.

The point of my answer is, what are you hoping will improve by upgrading ?

I recently moved from a 7D to the 6D but all me lenses were EF so it didn't cost me extra for new ones.

I don't really find much better quality with the pictures. If you can afford to change right now and have EF lenses then go for it.

If you have an aversion to spending money, full frame may not be for you. The lenses cost. If you get cheapo surplus EF lenses meant for film cameras, expect corner softness you wouldn't notice on 4 X 6 inch prints to be noticeable at 20 MP.

Number of pixels is low on the list of what counts. Check http://www.dxomark.com/Cameras/Compare to see how the sensors compare. Having the same number of pixels on a larger area sensor (assuming similar technology and processing) will give better noise performance, dynamic range, color depth, and a few other things. Big, juicy, pixels help. If you need to print huge images, then more pixels help, but your shooting parameters tighten up a bit.

However, more import is the skills of the photographer. Give me an expensive camera and I can take horrid pictures without trying.

One other thing about lots of pixels, your skill as a photographer needs to be improved and the lens quality needs to match, or be better, than the pixel density. Putting a crappy lens on a 36 mP DSLR will still look fuzzy.

Yes.

You will be stepping up a notch from mid-level to high-end. You won't notice any difference in the pictures you take but if you know exactly what you are doing, shooting will be much easier with the better camera.

If you're happy with the 60D what else matters? I don't use any of my Canon dslrs for video, for that I have a dedicated Sony video camera and even though it can also take 10 meg stills I've never tried it, for that I have the dslrs. Different horses for different courses.