I know this is kinda late, but I'm going to take the "con" here. I say you should do your best to win this cup game.
You said it yourself: your league is all bots and inactives. Which it is. This cup game could be the only meaningful human game you get to play all season. And you're going to mail it in?
And why? To save enthusiasm and game shape for... well, what exactly? Again, your league is all bots and inactives. You've got all spring to regain whatever you spent trying to pull this upset. Besides, how are you going to learn how to use CT and TIE if you never experiment with them? And now's the perfect time, when you've got no human competition and a long time before your next important game. Getting promoted is all about winning your league playoffs... which start in mid-June.
If your league had more humans in it, then yes, I would agree with the other posters who said it's more important to conserve resources. But I don't see what going for it costs you. But I can see what you'll gain if you win: $50,000. And your fans will love it, which means your Fan Survey will go up, which means you'll sell more tickets to other games and make more money down the line. And you might get an easier draw in Round 2 and win more cup games, which means more money and more fan happiness. There is much to gain.
And don't believe that you can't win. In last year's USA cup results, I counted six games won by a USA.V team over a USA.III team in the first two rounds. And I didn't even go through all of them. You're a huge underdog, the equivalent of a 15-vs-2 game in the NCAA Tournament, but victory is not impossible. You can look the games up yourself, but most of the USA.Vs who pulled this upset played Run and Gun or Princeton. Just sayin'.
I say, review the motivational speech of your choice (I recommend Bill Murray's "just doesn't matter" rant from Meatballs), set a gameplan, set your enthusiasm to Crunch Time and give 'em hell. At least play Normal enthusiasm, so you can see where you stand against a strong team in a meaningful game. Bottom-tier and new teams have a hard time getting a game like that. You've got a real opportunity here. Whatever you decide, good luck.