In the two worlds I commish, I'd say 95% of the owners are at 0 or working their way to 0. Both worlds are for experienced owners only.
Short version on ADV: If you're not trading for 2nd year players, it doesn't matter. Development patterns are pretty straightforward and 3rd year players will have a recognizable pattern. Of course, if the owner has low training or poor coaches, he's restricting development but, because of the way HBD is structured, you can see the ratings of his coaches/amount of his training. Armed with that info, you can determine if he's hurt a player's development.
As for your own players, you can trust your HS/College/Int scouting you used to acquire them. If you deemed a player good enough to be the 13th pick using 14m in HS scouting, you should trust yourself. "Seeing" his projections won't matter, you have to develop him anyway.
All that said, if you're a guy who wants to constantly trade for young players, you can save yourself a lot of research time by having higher ADV. I think it's a bit of a waste but, if I were going to make 6-8 trades a season for 2nd/3rd year players, I'd probably want a good amount in ADV.
I guess that wasn't that short.