For me personally I wanted that vigorous course load for a couple of reasons. 1. It'll help you transition better to a dental school curriculum which will be far more rigorous than undergrad. 2. It'll give you another talking point in your interview about how you improved your time management and could handle a busy load... I also wanted to show myself what I could manage and still succeed with. I'm more of a go getter and have high goals so I guess that's just more so my personality
When I look at students who are taking an easy course load, don't have a job, drink on weekdays and maintain a 4.0, I just don't see how that will catch the eye of admissions. I'd much rather interview and accept the applicant who took 18+ credits, worked a job, volunteered, shadowed, was in a club and could actually communicate like a human. I saw too many genius students who were just about smarter then the professors but also had their face in books on Friday and Saturday nights and had no form of social interaction.
If I were in your shoes, I would either take more courses and challenge yourself or at least do more in your off time to add to your resume/self enjoyment. High GPAs and Dat scores will catch their eyes but what they see as they dive into your application is what will convince them that they need to grant you that interview.
ALSO a lot of programs have a list of courses that they highly recommend to applicants so maybe check those out!