"Well, you can't farm Mystic Coins. The best you can hope to do is steadily earn them, at a rate of 1.66 per day maximum. At their current value of around 12-14 silver each, thats around 21.5 silver you're earning (or saving, as it were) per day.
If you were to run almost any dungeon, say 1 run in 30 minutes, you should pull in 1g without issue. Use that 1g to buy Coins, and you're up another 7 coins.
"But Ralcore, if I spend my 1g, I won't be saving any gold!" Well at first glance, that may seem accurate, but consider the Inflation GW2 experiences on a daily basis. The Gold you have today is worth less tomorrow, and even less the day after. By investing your money into Mystic Coins (a commodity likely to keep pace with inflation) you get them early at a lower price than you could obtain them at later, plus retain the ability to dump your stock at any time to recover your funds, with potential for profit over time."
Yea but i barely have 1 gold, and no one ever does a dungeon in the guild, so that wont be very useful