High pointed players (as in Tier 4 & 5), of course have more gold. They can easy set the prices of diamonds. Low pointed players can not afford to buy 25 diamonds (> 500k gold). Maybe it would be better that diamond prices be influenced somehow by your Tier and level.
You have some point here... It is true that the more players that are high tier and gaining more gold they will be the ones who sets the prizes... And that is why they "destroy" (according to some players) the game. But how will be he prize of diamonds will be relevant to tier, if for example they do something like potions and objects what will stop a player with diamonds to sell them at high tier (and gain more money) from selling them at low-prise tiers? This will create a huge supply of diamonds, at hight tier, and this will drop the prise, but at low tiers there will be lack of diamonds and it will sett the prises to the sky...
About the other issues of the topic, non-premium members are more difficult to develop. There is no secret about it, but it is not impossible to do it. A premium player have 24 moves per 24 hours and a simple one have 12, so is about the half... I do not seeing anything unfair here... And coz i am a moderator yes i have a premium account but i am playing the game and with simple accounts... We know some issues but believe me is too difficult to suggest solutions that keep the balances...