the main problem here is tiers as i said before raise the ratio conversion:
revenue daily-the way all faucets games works..... as i know this is a kind of faucet
lets say revenue 0,10 bitcoins ..... soo you can set the ratio on that day lest say 150 gold 10 satoshi
other day revenue 0,05 soo ratio could be 275 to 10 satoshi
other day revenue 0.2 bitcoins --soo you can set the 100 gold to 10 satoshi as well
and yes you could put some kind of fee inside the marketplace soo when a user buy satoshi or others would pay..... lets say the normal fee is 5% at almost all games and yes could be a buy as sell marketplace as this on this game take a look
http://virtconomics.comhttp://www.marketglory.comjust login or regist there and see the solution to all problems that may occur if you stand with the tiers bonus.....
as most games there they admins put a price on gold ,the users as wanna money will buy soon ,the more they buy later they can sell gold to boost the upgrades as that will raise day by day,soo lets say we can mine gold that will be traded to coin named mybitmine that will have another market to trade them into bitcoins....
lets suppose the coin on the game mybitmine conversion rate -------1 mybitmine around 500 gold and to convert it to satoshis lets say 1mybitmine coin to 50 satoshis soo something like this would allow all to win money invest or not at the game ,soo lets say the round would be infinite but the cost to upgrade would be the same as the current version ,that will take around 2 or 3 months to reach some kind of income good... and why not to allow unlimited miner as gold mines as trade carts but as the game need to sustentable those would cost several ,as you could set a maximum level to all upgrades soo say all users would be able to win together around 0,05 to 0.10 all weeks as the revenue is around 1 or 2 btc montly with the capcha back you can earn it easy,as you could add some other ads my sugestion use adhits here put a price at your spaces of advertising and let us users make the rest the support .... and yes keep the bitcoins ads ,but should choose the better payouts overthere.... main sugest is to you reconsider all requests and try to put this marketplace will make all happy again... and no one will be leaving the game investing 0.03 or investing 0.10 or 0.0002 doesnt matter you have a comunity supporter players soo think before take a huge step.