Well, my experience is from USNA, but I imagine it applies at USAFA, too.
When it comes to validating, you have to consider two things:
1) Validating as much as possible will free up your curriculum and course load during LATER YEARS, so you can take electives you like, retake courses you messed up, or just blow it off and coast.
2) Validating tends to push you into harder classes during Plebe Year, where the pressure is extremely high even under the most nominal courseload.
So, if you think you can handle advanced courses during Plebe Year, then it is definitely worth your while to validate everything you can because the payoff later is really worth it. If, OTOH, you are not certain that you can handle advanced Chemistry, Differential Equations, and whatever else ON TOP of being a Plebe, then maybe you'll want to coast now.
Your call. Just understand that you really only get to make it once, so make it count.
Good luck.