We all know how hard it is in games like these for newcomers to try to compete with veterans who started the game months or even years ahead of them. After climbing above the all dormant players and the part time players, they will hit a ‘glass ceiling’ above which they cannot go unless they are prepared to pay. So, after a while, they quit.
A better way would be to give them a chance to catch up and close the gap on those who joined before them (who already benefit from higher rewards, and rightfully so).
One way to do this would be to gradually lower the cost of upgrading common creature ranks and abilities in terms of the amount of gold and ability dust needed. The reduction could be 0.25% of the current price per day, leading to a minimum price of 399 (since 0.25% of 399 is less than 1, so it would not fall any further). Rare creatures could drop at a slower rate of, say, 0.1% per day while epic and legendary creatures would not deflate at all.
Once the gems had been collected, it would then be much easier for new players to become reasonably competitive, while veterans can still choose to spend higher amounts early to get the newest creatures if they choose to.
Any newly introduced creatures could start the deflation process a few weeks after the initial introduction and after any boosts have been removed.