Your divorce settlement was generous and, after 25 years of marriage, I have no doubt that she functioned difficult helping to raise your kids. You would, of course, know more about that than I. Congratulations for doing the right thing when so many divorcing partners can’t see beyond their own resentments.
Your divorce settlement also gave your kids peace of mind, which is difficult to put a price on. Whatever the nature of their relationship, I assume they love her very much. It’s difficult to untangle oneself from the emotional ties as well as the financial ties, but you seem ready.
Once you make a settlement in a divorce, it’s difficult to revisit it, especially if there were no conditions set at the time. If a divorce settlement doesn’t stipulate that the lower-earning partner had to discover a full- or part-time job within a certain period, it’s often difficult to change.
Including “modifiable maintenance” in your divorce settlement was a smart move on your part and, given your wish to reduce it, is a good start. That, and the fact that the rest of the settlement was generous, will bode well for you if this gets to court.
Your wife might argue, with reason, that she was married to from the beginning of your career throughout the peak earning years, and raising kids and managing a home is a full-time job, and a significant one, in itself.