Another variable here is the price of concrete, which I was just told yesterday is around $300/yard^3 in the valley. This is double what it was just a few years ago and the shortage is probably caused by sheer demand and SLC's geographic isolation. The new planned mine in Parley's Canyon, which is being fought by the cities and SL County, would probably help alleviate the cost of building. I'm not advocating for it but that's certainly an argument they are going to use.
To be honest, the towers are less important than the connectivity, livability, and affordability of the downtown core. I'd like to see some more transit improvements, green space, policies that benefit small businesses, and more mid-rise housing to replace the dead zones. Projects like the West Quarter, Post District, and the Greek Orthodox development are just as exciting as Astra or Worthington to me.
That said, a 500-600+ footer would really take our skyline up a notch. Here's hoping we see one this decade