Nothing is absolutely necessary! Players have reached the very highest level taking many different paths.
The thing that is vitally important is having the required talent and visibility. One without the other doesn't work.
It doesn't really matter whether the player wants to stay local for college or travel across the country. The more interest a player creates the better opportunities he will have. So if the local college is offering 25%, what would they offer if you were being recruited by several other colleges?
Years ago in our home state (Iowa) most every talented player would end up at a state school. Mostly because the high school season was in the summer rather than spring. Most Iowa kids never left the state to compete. The state colleges could sign them for very little money or offer preferred walk on and get them. Now those top kids are playing all over the country against the best competition. Now the best talent from Iowa ends up at places like Southern Cal, Florida, Baylor, North Carolina, Stanford, etc. If Iowa wants them they have to compete and fork out an attractive offer.
I use the above as an example, but it is true everywhere. It's really simple... The more people who know who you are and like what they see... The more valuable your talent becomes. Others might get disagree, but we see it over and over every year.
I actually see it differently than some. Often I hear this said... If you are a stud you don't need to do anything. To me it should be... If you lack talent there is no need to do anything. The player with exceptional talent needs to be seen as much as possible. He needs to be seen competing against the best possible competition.
Do the research! Look at the first round picks or those that committed to top college programs. These would usually be consider the top prospects. Find out what they did while in high school. Regarding this topic, find out if they played "Travel Baseball" and at what level of Travel Baseball. Almost all of them do!
So is Travel Ball a necessity? No, only necessity is having the required talent and making sure people know it. If they know it they will make sure they go to see it. All baseball levels are important and all situations are different. But I would have to think long and hard before recruiting a player that is taking the summer off. Last time I looked, the summer was smack dab in the middle of baseball season! If you're a good player, you should make the most out of the summer. For the majority of top HS players that does involve Travel Baseball.