The value of the 25% for Royal Mint is relative to the base rate. So if you've got placer mines (+10%) and almagamation (+20%), then the card is actually a bonus of 19%, or +1.9 more vils on coin for every 10 miners (if you look at it like Humility).
A villie with the +30% market ups will collect 1000C from a mine in about 21:20. The 1000C shipment is worth that much minus the 2:05 it takes to collect; so it's worth around 19:15 villie-minutes.
Royal Mint's additional +25% will allow 1 vil to collect an additional 1000C in around 111 minutes.
If you have 10 vils on coin, Royal Mint begins to pay off in about 11 minutes. If you have 20 vils, it's about 5:30, and for 30 vils, it's around 3:45.
That's why it's better to send gather rate upgrade cards when you have more villies, since it pays off faster the more villies you have gathering. If you're talking about a 20 minute game, you're hitting pop around then, and you probably have 30+ villies on coin, so Royal Mint pays off pretty fast vs a crate or unit shipment.
cue[This message has been edited by cu3hara (edited 12-03-2007 @ 09:21 PM).]