A day pass to the Amtrak Legacy Lounge is available to coach passengers for $20. To get access to the Metropolitan Lounge, you need to be a business or sleeper class passenger (coach passengers can buy a day pass for $50, I think). I would consider upgrading to business class. It's probably less than the $50 pass, and the on-board perks are pretty nice.
Changing to business if available for a portion or more of my trip was generally not much more than $50 for me . It afforded me access to the lounge when I did not have a sleeper...worth checking into.
Not exactly an answer to your question but unless you have a really long wait I don't think it's worth $50.
I just traveled around Thanksgiving and it's gone up to $50 for a day pass if you don't have a sleeper car. This is copied from Amtrak website. Chicago Metropolitan Lounge We've more than doubled the space of this now two-floor lounge and added many new amenities for customers who travel to and from Chicago Union Station. Amtrak customer service representatives will check your baggage and later pre-board you from the lounge to your Amtrak train. After stowing your carry-on bags, relax, enjoy complimentary snacks and beverages, or even take a shower. There's a space for kids, WiFi and power for your device or tables and work stations if you want to stay productive. If you'd like to use the Chicago Metropolitan Lounge and you don't already have it included with your reservation, you can buy a day pass to get full access to all the lounge amenities for $50. Just see a station agent at Chicago Union Station to buy one.
Thanks! Your answer is awaiting moderation.