Advanced is not just other team's players, it also involves your own players. Higher ADV scouting budget, the more accurate the future projections are. A couple caveats - pretty much after age 27 or 4 seasons, whichever comes first, the player will pretty much be whatever Current says, with projections out the window.
Many of the veteran owners have enough experience to do their own projections so they zero out the Advanced Scouting budget. They can tell, based on Current values, age, experience (and some other factors to a lesser degree) where the player should end up when done developing.