Longtoss:
Excellent question and topic starter. To avoid it being hijacked further, let me add my 2 cents. First, my comments will be limited to middle infielders because that is what I played and know something about and that is what my son plays and so those are the players I tend to watch at showcases, etc. Compare and constrast as my High School English teacher said year ago. Second, realize that my conclusions are tenative and not yet constructed in stone because I have not seen the final outcome of my observations. However, here goes.
Overall I believe the trend to scouting at more showcases is a good thing. Not necessarily for MLB but definetly for college coaches. It has its negatives; the most egregious is that the finiancially straped families with the outstanding athelete are left out of the loop. But it provides any interested college coach an opportunity to see many players at many positions in one place at one time and competing against each other and that is a forum where the talent on display can be evaluated.
The question is what did the player's overall participation at the showcase tell that college coach. Regardless of his ability to "showcase" his skills on that day, the perceptive college coach observed the players attitude, his ability to deal with stress and, perhaps, adversity. He evaluated how the player mixed with the other players, how much of a team player he was, a potenial leader he was, etc.
It is true that many coaches are not watching for these traits. They come to the preliminaries, write down the "pop times" and the gun reading for the throws to first, some hitting and leave. Others come to the games and read the sheets on the information of the preliminary events. Then the game times come and those coaches that are still there may see a player at his best or at his worst and the evaluation is accordingly made. As PopTime has pointed out in his post, the perceptive college coach will know this fact and will want to "see a larger sample or body of work before they commit one way or the other" to the player. How many coaches go through all these hoops. I would say not many.
And, as a result, you have the situation WillieBobo describes. Players with great pop times and gun times to first that make an accurate throw one out of 4 times on their best day. That, by the way, is a fielding % of .750 which should be unacceptible to anybody. But, say the defenders, you can teach a 17 year old boy to throw more accurately: you can't teach him to throw harder. WRONG AGAIN BOZO BREATH. The perceptive college coach will understand from watching the player whether he can get his arm speed up with better mechanics, etc or whether it will be dificult to improve the accuracy for the 85 MPH guy who has no range and and can't consistently catch a ball backhanded in the hole.
Reader of this posting. Will your son be evaluated by such a coach at a baseball showcase near you? Doubtful but enough in the realm of possibility that it is worth the risk. Because the preceptive college coach is the one you want your son to play for.