There are numerous teams in my world who have zero Advance scouting budget yet are very active in trading.  It appears to me that they must have a decent idea of the other teams' player ratings b/c the trades seem reasonable, or they even have an advantage at times.  Is Adv scouting really necessary to accurately tell the quality of other players and their projected ratings?  

So it doesn't affect how accurately you see opponents' actual ratings?

No.  ADV scouting only affects projected ratings.  Everybody always sees the same current ratings.

That seems like a shortcoming.  ML teams have scouts scouting other teams all the time, and especially when they want to trade.  A recent example in Boston is Kevin Youkilis.  A well established veteran, yet teams scouted to see whether he could still contribute.  Why would another team have as much information as that player's current team?  For example, how would another team (without scouting) know an opponent's makeup, patience, work ethic, etc.

This has been discussed in the HBD Suggestions Forum.  You should bring your comments there.

http://www.wisjournal.com/forums/Posts.aspx?topicID=447270

A bird in hand is worth two in a bush.