My son's too young yet for me to claim great knowledge about how PG showcases and WWBA events do or don't affect MLB draft status.
BUT:
We've been to WWBA events. Without question we saw the nation's best. Your kid can play in the local travel circuit, in Legion ball, or on his school team, but until he matches up against the nation's best, how do you know how he really measures up?
I can say that WWBA/PG exposure has led to a sudden influx of mail in the household from coaches at top line colleges. Some standard camp brochures, to be sure, but lots of personalized, handwritten notes. (It's enough to make a teenage boy's head grow a few hat sizes, but that's a subject for another day.)
We haven't been to any other showcases yet, so you can't give the credit to anyone but PG at this point.
As someone said above, THAT'S THE FACTS, JACK!