Do you really like negligible depth of field? You get more out of focus blur for a given aperture with a full frame. I love shooting at f/1.4 to f/2 (35 to 55mm FL) and f/3.5 (180mm macro). That is one of the big advantages of FF. If bokeliciousness is not your style, APS-C is more than fine. The FF cameras tend to have about 1 to 2 ISO doublings advantage in noise - my 60D is getting quite noisy at ISO 1600, the 6D equivalent is 6400. If you don't shoot at high ISO, APS-C quality is fine. I use the 6D with primes for landscapes and high ISO shots, including astrophotography, and use the 60D (maybe soon replaced by 7D2) for one-lens shooting (EF-S 15-85mm f/3.5-5.6, quite a good lens, probably better than the 24-105 on crop), for macro, and for action / birds. I don't currently have a normal zoom for the 6D, and I use a mix of old film all-manual lens classics (sitting around the house) on adapters and digital era primes.
There is no one right answer.