Phoenix' problem is that their skyline stretches two-miles between downtown and midtown. So, the gap between the two is pretty darn evident. I think their skyline would be significantly more dense than Salt Lake's if their downtown/midtown covered the same amount of space as Salt Lake's.
Portland's skyline - well, I don't see Salt Lake passing it anytime soon:
The problem with Salt Lake's skyline, and something that will continue with most these proposals, is that it's:
1) Boxy as fuck - even Tower 8 is basically a box when you get down to it.
2) Too similar of heights has created a ceiling effect. Salt Lake's tallest is 422 feet. When Tower 8 is complete, six other towers will be fewer than 100 feet smaller that the Wells Fargo Center. That's not a horrible thing if the skyline had a signature tower - which it does not. San Diego is a skyline that is very capped at a specific height and it runs circles around Salt Lake due solely to its diversity of towers (going back to point 1):
3) The layout sucks. Some of this is due to the wide blocks, which allows for significant gaps in the skyline (especially when you couple it with the city code about mid-block high-rises) but some of it is also due to the fact Salt Lake's tallest almost universally have been built on just two streets: State Street and Main Street. That means the skyline doesn't spread out over the downtown area like many other cities.
This is extremely evident in aerials of the city:
Compare that to Portland:
There's much more density and the skyline is spread out over a sizable amount of streets (their small blocks help).
But one thing I think has hindered Salt Lake, and hopefully it'll change as the skyline begins moving off of Main & State, is just the overall lack of density once you get off those two main streets.
It's almost non-existent, especially on the western area of town. Sure, there will be projects (like by the Viv) that will help change this (along with the convention hotel) but there has to be more than just these four-to-five story residential buildings and hotels.
Currently, and with those three under construction towers, SLC has 17 towers between 200 and 300 feet (not counting the Capitol, but counting the City-County Building + the LDS Temple) downtown. Portland has 30+, and that's on top of their three 500+ footers and other two buildings that rival Salt Lake's tallest (or exceed): Park Avenue West, which is 460 feet and PacWest Center, which is 418 feet. In fact, Portland has 18 built, or currently under construction, buildings of 300+ feet. Salt Lake has 14.
So, we're still lagging...but we can make up some significant ground in the next decade.
My hope is that we get a proposal for a 400 footer south of 400 South, or at least west of Main Street.