Yes we were going to rent a car in Colorado Springs anyway. I think if No. 6 is exceptionally late and arrives after the light rail has stopped operating we would probably take a taxi or uber to the airport and still pick up the car and head for Colorado Springs. I don't relish the drive to Colorado Springs in the wee hours but as long as we can coffee-up, we should be fine. Of course if we know well in advance that No. 6's schedule is a disaster we may try to cancel the Colorado Springs hotel for the night and stay at the airport (depending at the cancellation policy of the place in Colorado Springs.)
There's lots of good info above and I know I'm sounding picky, but the A-Line is commuter rail, not light rail. Commuter rail is run with FRA-regulated equipment and procedures and has PTC. It's limited to 79 mph, runs in Colorado under 25,000V AC catenary, stopping at high level platforms. Light rail evolved from streetcars and interurbans, has ATS and CTC, in Colorado runs under 750V DC catenary or trolley wire, stopping at low level platforms. Commuter rail lines (A, B, G) in Colorado are run for RTD by a private contractor and light rail lines (C, D, E, F, H, R, W) are run by RTD with union operators. The commuter ra il N-Line now in the test stages is to be run by RTD.
It's all under one tariff, but the main reason for referring to them separately from a customer's point of view is a much higher degree of speed, comfort and baggage space on commuter rail, while the light rail is able to get much closer to where commuters want to go. The airport station is a convenient commuter rail exception, because the line was sketched into the original Denver International Airport plans.
An easy way to remember them: at Union Station Tracks 1-8 are commuter rail and Amtrak, Tracks 11-12 are light rail. Numbers prefixed with "B" are the 22 underground bus gates.
For readers elsewhere: commuter rail cars in Colorado are younger sisters of the SEPTA Regional Rail cars in Philadelphia. Light rail cars in Colorado are younger sisters of San Diego and Sacramento cars and daughters of the original Frankfurt, Edmonton and Calgary cars. 2017 photo shows light rail R-Line connecting with commuter rail A-Line at Peoria Station. The ramp in foreground is for ADA access to high-floor LRV's. Low-platform LRV's have met for a late-night timed connection in the next photo. In the B&W photo, commuter rail customers enjoy high-level platform boarding. There are pluses and minuses to each.