The only way MiLB pay is going to improve is if every MiLB player refuses to play. That's not going to happen. 84% of American MLB players come from the first ten rounds of the draft. These players receive signing bonuses of six and seven figures. They don't need to worry about the money so much. If the rest, who typically don't sign for much want to walk baseball would tell them to have a nice life and replace them with those desiring to play for the existing pay. It's not necessarily fair pay. But it's the reality of a market based system given the rules organized baseball is allowed to use.
On a personal level I believe MiLB pay should at least keep pace with inflation so it's not less pay. In the past thirty years inflation has been 400%. MiLB pay has increased 75%.