I think travel is essential especially if the goal is to play top flight ball at the next level. But for the reasons you might think. The question you ask sounds as though you are focused on the exposure element and that question has been addressed throughout the thread.
To me, almost as important as exposure is the quality of competition question. In our experiences, playing travel ball, REAL travel ball is about kids getting an opportunity to play the game against the best possible competition. I argue that high school baseball, outside of a few markets (mostly in the Southern tier), the quality of high school baseball competition is really diluted and the caliber of the game is lowered. Showing out in the spring is irrelevant as a predictor of future competitiveness.
By contrast, going to travel tournaments (especially Perfect Game national events) gives a kid a chance to play against other kids with his exact talents and aspirations. Personally, I found watching my son hammer a triple against a kid signed to CSU Fullerton to be more gratifying than when he went yard in the playoffs against a kid who won't be pitching at the next level. Even our local summer league, as good as it's become, doesn't forecast as well as flying to GA and facing kids who are almost uniformly D1 guys.
My son has travelled (again, REAL travel) to five major events since 9th grade. Every time he made an all-tournament team, he brought something intangible back that lead to his recruitment and being named Captain of his HS team. So yes, those travel experiences were indispensible to his development.