There is a valid case for any format...APS-C, APS-H & FF. It depends on your needs. Your needs may require a $35k MF kit, so that's what you get. If your work goes no further than the web, screen viewing or medium sized prints, then APS-C will suit your needs perfectly. Maybe even a decent P&S.
Dr. Neuro mentioned earlier, "I'd miss the thinner DoF you can achieve with FF, for the same framing..." By the same token, there are occasions when the greater DoF can be very useful. I currently work with FF & APS-H (x1.3 crop) and will likely pick up a 7DII when they ship. They're all useful for particular projects or shots.
I often feel concerned when I read posts from someone aching to go to FF with the misconception that FF is this extraordinary Holy Grail from Planet Camera. Often the upgrade can be a disappointing waste of money. OP, go FF by all means, just do it with your eyes open. And keep your APS-C.
Lookout! Here comes my evangelical moment. Good workers never blame their tools. Gear Geeks and Pixel Peepers aside, the true Holy Grail of Planet Camera lies within the photographer. Great images are made by photographers, not cameras.
I have used both FF and APS-C sized Canon DSLRs. Certainly there is noticable difference in depth of field b/w FF and APS-C - but the difference in depth of field (DOF) between P&S to APS-C is MUCH larger! And when people say "FF gives a 3D feeling" or "the quality of light from FF is so much better" - it's probably as a result that the photos they've chosen (or seen) from people using FF were more carefully composed, timed, etc.
Sometimes I prefer the larger DOF that a APS-C can give for the same aperture (eg for macro - and sometimes for landscape). Other times I want a razor thin DOF, and then I use a fast (ie less than f/2 prime on a APS-C, which often does the trick. I've done the 'blind test' even with pro photogs many times, and without knowing the camera / lens, 90% of the time are hard pressed to tell if it's FF or APS-C - many people delude themselves on (potential) purchases, in marketing it's called "cognitive dissonance".
It sounds like the OP might be well served by the Tokina 11-16mm f/2.8, as this is both fast, and gives sharp results (also reputedly good wide open). I have a good copy of the Sigma 10-20mm, which is sharp corner to corner. Often I've been less than impressed seeing photos of the full frame equivalent (16mm) eg the 16-35mm, which have noticeable corner softness, even stopped down.
Not that I pixel peep, but there IS something to be said about using the 'sweet spot' of lenses (or specifically lenses designed for APS-C sized sensors, which seem to be very good on the ultra wide angle!) There is definitely a place for FF, but as PW wrote above, FF isn't the holy grail - it's in the photographer (knowledge, artistry and technical competence!)