Sorry folks, but I'm going to ramble on a bit. If you get bored, just shake your head in sorrow and pass on by
Nice photos of before and after, and I do think the pictures make the place look bigger than it actually is.
Don't know if you noticed the light fixtures, but in the before pics they are kind of ugly flat panels and the more elaborate ones that are in place today. The ones you see today are reproductions based on an earlier set of lights. The original set were taken down years ago because they were so heavy and the ceiling supports were deteriorating. During renovation they redid the supporting structure and, because the original fixtures were falling apart, had a faithful reproduction of the original made. They might not be the real thing, but I like them. You will also note in the after pictures that a few of the original benches were retained. Nice touch, I think.
That arch was removed years ago. In fact, probably the late thirties or early forties (don't quote me on that). While we often bemoan the fact that history is being destroyed, with good reason, we have to keep in mind that it has been happening for years. Centuries, even.
It's also good to keep in mind that Denver had more than one station, even after Union Station was built. Kind of like modern day London. Just a quick run through and counting on my fingers and I can think of at least seven that I have used, depending on where you're heading and which railroad you're going to use. Denver used to be that way. As rail traffic waned, so did the stations.
Through traffic at Union Station no longer makes any sense. When there were multiple trains coming and going the lines heading west out of the station would connect with the current freight lines for traffic headed south towards Colorado Springs, New Mexico, and connections with the mining areas of southern Colorado. Also connection heading northwest to Golden, Arvada, Boulder, etc. But it's hard to justify maintaining that much track with little to no traffic.
The current Y that Amtrak uses to turn around has been there for decades. The bottom of the Y not only serves Union Station but also the freight line that runs north of the station (you can see the trains or even walk over the thing) then curve to the south a bit further on. One part of the Y heads east through a yard and another Y, roughly running parallel to I-70 all the way to Limon. This is the route of the old Rock Island Rockets coming in from the east. At Limon the train would split, with part of it headed to Denver and the other part to Colorado Springs. [Interesting side not: the Rock Island had a modified B unit with controls and windows installed. When they got to Limon, the B unit would run into Colorado Springs and the A unit on into Denver.]
The third branch of the Y heads northeast through an extensive yard along Brighton Blvd almost to I-70, about where the Colosseum and Forney's Museum are (if you are ever in Denver, by the way, it's worth a visit) and follows hwy 85 north to about Brighton. Here it splits with a line running north to Cheyenne and the other running along I-76. This is the route of the old Burlington Zephyrs and the current Amtrak. When it gets to Brush, it divides again. Heading east through Akron, Wray and on to McCook is the Amtrak/Zephyr route. Continuing northeast it runs to Sterling, where it connects with the old Burlington Hi-Line, an on through Julesburg to the Big Springs Junction in Nebraska, where the UP City of Denver turned off with the other "City" trains heading west through Cheyenne.
Didn't want to get to complicated here, so I kept it pretty simple. If you do a sattelite view of Union Station in google maps, it can get kind of interesting.