IC
I agree - take it one step at a time. If your cadet wants to give an IC sport a try, I say go for it. He/she can evaluate it and decide if it will be worth it once there.
If there's real interest by the cadet, it wouldn't be a bad idea for the high school coach to let the academy coach know there's some interest. That way, the cadet may be able to start participating with the team from the outset. There were several "walk-ons" in my son's sport - the ones that were able to participate with the team during BCT (becaue the coach already knew to expect them) seemed to have a better chance of making the team. Some walk-ons continue throughout their 4 years there; others don't. (Same goes for the recruited athletes.)
If the cadet does make the team, is it worth it? That depends. Just like beign an IC at any school, there are costs and benefits. I would say that my son did benefit from the IC experience. It depends on the coach, the teammates, and love of the game.
As for helping with their later career - it can (but doesn't always) help with job assignments. The coach does get to provide some input (a form 94 I believe) for a certain number of athletes that is considered in the cadet's Board Order of Merit. (AOCs, officers over the flying team, and others can also submit form 94s.) Other than that, I'm not aware of any official career benefit. (But I'm just a mom - and from a non-military family - so others may know more about how that all works.) Non-official benefits may include meeting with alumni in that sport who are now active duty and touring bases when travellign with the team - my son's coach (retired military) has been very good about having officers from various fields come talk to the team and setting up base tours when they travel for games.