You're probably not going to see many upgrades at the 25K level at any of the three big domestic carriers. AA is the only one of those that still provides full flight miles based on distance, though that is going away sometime in the second half of the year with a date not announced yet. The one advantage AA has over UA and DL is that they do not have spending minimums at any of their elite tiers.

Take a look at Alaska. You indicate you want to fly both AA and DL, and right now they both partner with Alaska. They're not my primary carrier so I can't explain all the details of their mileage program, but check out the Alaska forum or the airline website. Might get lucky and have an Alaska flyer stop by this forum and explain their program in detail for a flyer that does 25K.