I'll weigh in on the side that stresses the importance of travel ball. I follow Cookeville soccer, and the level of success of both the boys and girls' squads has a direct correlation to club ball. The boys' squad has been to sectionals 3 out of the last 4 years, to state once, and has been ranked in the Eurosport poll the past two years. 90% of the Cookeville boys' varsity squad plays travel ball. While they play D-II, the six months or so of training they receive from that, as has been evidenced by recent success, has greatly contributed to keeping the boys' program at a high level. When the Cookeville girls' program was it its best (Charlie Hardee's team of '04 and Grant Kelly's team of '05), 90% of the girls played travel--and many of those went to Nashville or Knoxville to play their club ball. This year's Cookeville girls' squad had only 4 varsity starters who played travel ball. Even with talented athletes, it is extremely difficult for a team to contend if the majority of its players receive only the three months of training that comes with the high school season.
Fortunately, the Cookeville girls' travel program is getting organized again, and there will (hopefully!) be u-15 and u-13 teams in the spring.