I am going to give you some "golden" ideas that will increase your revenue. You've already got it good but you have some room to grow. So here it goes:
1. Just increase cost of medpack to 50 gold or make it so that a refill only gives 2 additional hits per refill. No worries Gree, you have people hooked. They can't give up their precious spots on the leaderboard. They view their (yours in reality) accounts as investments. They fear to lose on their investment by not continuing to do as they have in the past. So raise the cost and watch the money pour into your bank account.
2. Make a new option in the attack screen during WD. In addition, to attack and power attack, have a third option called lets say "Sneak Attack". This option requires a full health bar too but comes with a game of chance. You can have positive and negative rolls of the dice each time this option is selected. A player may increase their WD points on a single target by say 2x,3x,4X,5x, etc. But as with any game of chance you might could lose. Lets say throw in one 0.5 or 0.25 modifier and you get your points cut in half or by a fourth. People love a game of chance. This in addition to 50 gold costs for medpack. Watch the profits soar.
3. Make some LE buildings that not only require gold to buy but gold to upgrade for some high stat units. Quit giving away all these nice buildings for free. People will still buy them. They have to...too much invested for someone just starting out to be able to catch up on stats.
4. Add a small modifier to the end prize in normal and prestige mode LTQ prizes. Players love boost units. You have players right now not doing LTQs because of the fear of too much XP gain versus "poor" reward. Add some modifiers and watch the gold fly! And while your at it, stop letting the players outsmart you with this pre-staging nonsense. Reset the missions back to zero for all targets when you do the data push for a LTQ. Why let people get this stuff for free. Once again, the boost unit is the key to it though. Without the boost it won't work. More money, more money!
5. Boss events - same as #4. People dont spend gold on bosses because some can do it for free and others see other events with less financial demand to get same stat increase. You put a boost unit at the end of 50 bosses and i guarantee the dollars will flow! Yes some campers will get them for free but thats the beauty of it. Your top players above L150 will know this and will have to spend to get same boosts! Pure Genius!
Gree - I hope that my ideas have enlightened you and that I have shown you the way to increased profits. I love your little game and want it to be around a long time. I know it takes money to support it so i have given you this gift to ensure its survival!
If you need additional ideas, you know where to find me!
Service Announcement - compliments of the Evil Mastermind