Goose,
Sorry, but I do not know the answer to your question concerning the MWC selection process. Perhaps those in the know can shed more light.
The All Star game and the MWC may be great perks, but if nothing else, the NWSBT is a MUST for aspiring players. The event was free (partially funded by donations to list your player in a program) and was the most heavily attended event my son attended. It was literally swarming with college coaches and scouts. It was a fun time (at least to watch!). I would imagine it would be even more of a rush for the players.
Hope you find the answer to your question but if you are really a player, the NWSBT will get you noticed. The rest is just icing on the cake!
Good topic, IMO....