I think the substitutions thing is fine as is imo... and a lot of the 'faked injuries' are real cramp issues and such... but I'm all for making every player that goes down in the second half leave the game for an amount of time, you see SOME of this but not across the board... faked injuries and flopping are still real issues though...
the point that they (powers that be) aren't changing the rules for America fans is totally true, but in a perfect world two things happen that would grow the sport here in a hurry...
1.) Flopping, if a replay shows a player clearly flopped they get a match ban (like a retro active red card) for the next match... if it's a repeat offense then it's multi game and a heavy fine... and so on... that would halt that stuff real quick..
2.) Off Sides, to me, this is the thing that kills a lot of American interest... you could do two things to fix it, one, a lot of times if a player is offsides when the ball is released, but comes BACK ON before being the first to touch the ball that should not be offsides... when I see a player make a run, off sides, only to have the defender re gain ground before the offensive players touches the ball and the flag still stays up I cringe, soccer would do itself a great deal by taking the NHL approach to offsides,... Also, if ANY part of the offensive players is on, the players should be considered 'on', basically, give the offensive player the benefit of the doubt always, they (referees) are supposed to do this but don't... I think that would help the scoring and thus the interest without drastically changing the game world wide.