Since I had a hard time figuring out the Coin-Drop weapons bought from the Marketplace, I thought I should share my findings for anyone considering spending Station Cash on one.
The Coin-Drop weapons have a "+25 Coin"-stat. This does NOT mean a 25-coin increase in any pile of cash you find, but a 25% increase in money gained, on average.
Quote customer support:
"In a normal dungeon, let's say you get a total of nine enemies dropping four coins each, on average. With the coin flow weapon you'd get eleven to twelve enemies dropping four coins each, on average. Without the coin flow weapon, you'd average out to thirty-six coins. With the coin flow weapon, you'd average forty-four coins."
The increase in money works for quest-rewards as well, if you have the wepon equipped when you turn them in.