I've been playing since the days of no level requirements on any of the buildings so take these suggestions as you will
1. Stat inflation must be carefully considered. Right now the game is totally out of balance. You need to have valor, cash and gold units all with in about a 100 point range of each other. Since we get a ton of units with stats in the thousands we need cash and valor units in the thousands. You don't have to balance the old units, just provide new units to purchase using in game cash and valor.
2. Consider the cost of gold versus the return on investment. Right now buying gold units is useless. Inflation renders them obsolete before a WD cycle is even completed. Your gold buildings and defenses are similarly useless due to inflation. That really just leaves health refills the only sense able use of gold. When I started this game people would talk about making purchases of units and buildings to give them a slight edge over the competition, now gold only has one use and it alienates many different styles of play that Modern War used to accommodate.
3. Since the start of the game leveling has been undesirable. Consider placing unit buildings and boost buildings at higher levels to be unlocked. I've been playing since the start and have skipped over a lot of content because leveling was such a disadvantage. If I had more and more content to unlock and build I'd level up gladly.
4. Have a way to clean and sort your inventory. My tree snipers have been riding the bench for years. It is time they earned their keep.