We are currently commuting weekly between Toowoomba Wellcamp (WTB) and SYD, and all the flights are on Q400. Generally I get 3A or thereabouts (status helps) and a shadow. What's REALLY good about the Dash 8 is that the seats don't recline, and the pitch seems slightly better than 737. Outcome is that even without exit rows, there's room to use a laptop comfortably, and plenty of space under the seat in front.
Also: the premium hand-luggage thing is very efficient and can actually work for you - if hand luggage isn't weighed at SYD, then you can effectively get an additional small bag. Which brings me to the real challenge.
The QF website states that Dash-8 services are limited to a single check bag at 23kg, which is quite a restriction compared to the SG/WP expectation. I discovered that after four years of routinely checking two bags up to the 32kg limit. It's never been questioned, but there it is on the website. I **think** the Dash-8 restriction might be more in respect of -200 or -300 planes, but I can't find anyone to ask (and I don't actually want to ask because I might not like the answer!). Getting any contact with Qantaslink or Sunstate is going to be beyond mere travelling mortals.
Anyway, my vote is positive for the Dash-8 experience. Just don't sit anywhere within a few rows of the prop - noisy and not fun. At the front or at the back is fine.
Matt, thanks for the useful rundown.