justloveit,
No one could ever answer your question unless they have been there. Seeing that I have been to every one of them, I’ll try to answer.
It’s probably not as important for sure first round picks as it is for other top level players. It has proven to both increase and decrease draft status. You definitely need to have something that will interest MLB scouting departments. Most of the players that attend end up getting drafted or go on to play at a very high level of college ball.
The key to the National Predraft is the number of national cross checkers and MLB Scouting Directors, even some GMs that have attended in the past. Typically these people only see the very highest profile prospects.
Many, if not most, of the players that attend have been seen by many scouts before the predraft. For most of these players it will be the last time they are seen before the draft. For some it will be the only time they are seen by the heads of MLB Scouting Departments.
Those players who have attended in the past include current Major League players like Carl Crawford, Brian McCann, Ryan Sweeney, Joel Hanrahan, Jeremy Hellickson, Tyler Clippard, Jonathan Arencibia, Jeff Clement, and several others.
As far as importance, I can say it ended up being very important for some and it might have been better for others had they not attended. The importance is based on what the player shows. However, the one thing it does always show is that the player is interested in being selected in the draft and is signable for the most part. Otherwise why would he attend a predraft camp in Iowa a couple weeks before the draft.
