I college mentorship is an excellent way to boost the learning and enjoyment of a high school team. The college students will generally know more about what will or will not work than the highschoolers and can offer great insight and guidance. The also can sometimes get access to the colleges workshops if they are already associated with a group in the college that has access, thus being able to do more precise or detailed work than would otherwise be possible using the highschools resources.. however that much you probably already knew.
I do want to caution you about these high school college relationships as there can be a detrimental downside that i am in the process of trying to overcome with a team i recently started working with. That is the college students sometimes offer to much guidance to the point where rather than teaching the high schoolers how to do stuff and suggesting what to do, they instead take it upon themselves to just completely build the robot on their own. This kills the interest of the high schoolers, makes the building phase fairly boring, and just overall takes away from the enjoyment and excitement that go along with the 2am building sessions and the caffine highs required to finish ontime. I highly recommend and encourage high school college relationships but make sure the college mentors know that they are there to assist the high schoolers, not to do it for them. also i'd recommend regular "reality checks" for the college students to see that they are not getting over-involved.