The point I'm trying to make is, if you have a coach committed to the program, teaching the game, and creating a challenging and enriching experience in the summer, then high school baseball is the best option. If the high school program just throws the team together, gets someone else to coach it, or just schedules games without using the time to teach, then I think those teams probably should just take the summer off.
If all the things mentioned above are done, then it would most likely be worthwhile. Kids have plenty of time to work on their swing in practice. They have plenty of time to work on their fielding if they practice. Travel ball does not in any way prevent practice.