1) There is no reason why an APS-C sensor is less sharp than a Full frame, if the pixel density was comparable. If the pixel density was the same and the quality of the glass the same sharpenss would be the same. In the end, you can take a photo just as sharp on an APS-C sensor, but you will have to be more careful abou the lens, the lens settings, and technique.
2) Yes. But again, this depends on the pixel density. if a FX and DX sensor have the same density then they will have the same noise performance under the same technology. There is currently about 1-1.5 stops advantage in a 12MP FX compared to 12MP DX sensor. For landscape photography this has no bearing.
3) Yes I agree. But it is not as if you have no reasonable DX options.
The Canon 10-22mm is ok for most.
4) Yes, bigger viewfinder is great, but wont change the quality of a photo (but maybe the probability of a well composed photo)
5) This isn't a reason, Focal lengths are easy to adjust. And in any case you are wrong. The lens is the stated focal length on crop, just that a crop sensor does just that, crop the image.
6) Better dynamic range, again depends on pixel density. If it is low like the Nikon D3 then the full-frame sensor will outperform. But you need to know how to make use of this DR.
Then don't forget the negatives:
Heavier, more expensive, heavier lenses, more expensive lenses, heavier more expensive tripods required, more expensive insurance, larger lenses with larger front threads and making more expensive filters. A heavier camera you might not take with you. Less reach for wildlife or sports photography (compare size and cost of 70-200 2.8 and 300 2.8). DoF is relatively shallower, which is not always a good thing.
1. Over my head
2. Over my head - yes I am a little out of my depth here
3. Fair enough, I guess this one is subjective
4. Again, probably subjective, personally I love the bigger viewfinder
5. Perhaps I worded my point incorrectly
6. Fair enough
As for the negatives,
- Weight - I am a bit weird in that I prefer the extra weight of the body/lenses
- Expense - Yes, this is tricky to deal with especially when you're not made of money, but then you get what you pay for. If you're prepared to pay a premium then you will notice a difference. Much like if you bought a £50,000 car instead of a £5,000 car, it will cost more to run, insure, buy parts for, but if I could afford it I know which I would choose.
- Heavier camera that you might not take with you - At the moment I have my camera with me every day, and it is accessible all day every day, although I appreciate not all people will do this.
- Reach - This is subjective, I don't do wildlife or sports, so I don't need it. For a wildlife or sports photographer then of course this may be a negative, especially if on a budget.
- Shallow DOF, personally this suits me.
I think all of this is down to the individual to be honest!
As I said, it was an uncontrolled, single test, by one individual, so I'd take it with a pinch of salt.