If it were up to me each round would have some change, one of each per round possibly, or a mix of some:
1: all stats bonuses would be 50%
2: one round the gold would be 10-20 times more per soldier.
3: UP costs only 1,000 gold per upgrade
4: a round with no arenas.
5: a round that lasts 1 day, and everything costs 1 gold, but you only get 1 gold per soldier, lol.
those are examples, it would take good coding to do, and time to do it, but it would change it up, as it is, you buy UP for 20 days, then build up your first 2 stats, then near the end train down as many unused soldiers as you can to get spies for rank.
unless your like me and get bored and go for max SA, then get bored remembering back when SA was in the billions.
But I'm going for rank, or at least holding capital, if I get bored I may do what I used to and go play in border and stay there for a few rounds.