Interesting views. We've just purchased an MK3 and have both the previous generations in the family.
I can't say I agree with a lot of the points you mentioned but this is subjective so, each to their own opinion.
For me, the MK2 feels more spacious than the MK3. There is better headroom and the sides don't cave in as much. Headroom wise, the MK1 is the best of the lot. There is more leg room in the rear of the MK3 but this is at the expense of boot space - which is noticeable. It was one of the first things we noticed. The MK3 boot is much smaller than the previous generations.
Seats are about the same, I'd say MK1 seats are most comfortable but none of the Jazz seats are particularly supportive if I'm honest. The ride doesn't feel like an improvement over the MK2, it may even be marginally firmer but certainly not more refined.
I find the MK2 the quietest of the 3 generations with the MK1 the loudest but there isn't that much difference overall.
I too prefer the MK3 dash design but the infotainment system in the MK3 is a good idea let down by the software. Some of the controls could be far simpler. Take the cruise control for example, I still have no idea how to operate it, despite having used CC in other cars for many years!
I hadn't noticed that the wing mirrors are narrower on the MK3 but we really do not like the way the mirror tapers and curves down at the ends as it makes it harder to see. We much prefer the older mirrors which have a larger mirror area making it much easier to use.
I can't really comment on the MPG as we haven't had it long enough to say but we haven't noticed any difference in consumption between our 1.4 MK1 Sport, 1.4 MK2 and our 1.5 MK3 Sport (all manual).
The gearbox seems a little stiff in our MK3 (although it could be down to the low mileage), reverse gear is not always easy to engage unlike the MK1 and 2.