I'm with cedwards, get the call right.
I favor assigning another umpire to be up in a booth to monitor every close call/controversial play, except balls/strikes. If the ump sees an obvious blown call (irrefutable visual evidence, a la NFL), he would radio down to the home plate ump.
No challenges given to managers, though. Let the professional umpiring crew (wi the video replay ump in the booth) do their job to attempt to get all calls correct.
And as far as instant replay taking too much time or slowing down the game, a review would certainly take a lot less time than suffering through another inane on-field tantrum thrown by a manager. Reply would probably would actually speed up the game.
manager
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