Unfortunately, the replies were posted after I had already completed my trip.

In any event, I did end up taking the metrolink to see the Arch. The trip there wasn't bad, but the return caused me to wait a lot longer than the outgoing as a lot of people started boarding the train to see the baseball game. Yes, the time was really tight, due to the delay in rail service on my return. Funny thing was that my flight was delayed by 30 minutes, so I still ended up with some extra time.