Whether you pick a SMP or a post-bac or a graduate school (JHU) you should go should largely depend on your uGPA and basically nothing else. Drawing from my own personal experience and students I've mentored & seen, general rule of thumb is if your gpa is <3.3-3.4, anything short of a SMP will probably not help you get into medical school. This is esp true if you failed to get into medical school on your first (or more) attempts. The other thing I'd caution you on is that the name (fame) of school =/= strength of their post-bac/SMP.
Also, remember that the people who you talk to will always be those that represent the most successful in the respective program (that includes me.) I also had to deal with the JHU dilemma 6 years ago when I first was applying to post bacs (I got accepted into all the post bacs I applied to). I talked it over with the JHU people (as well as the harvard extesnsion) when I was choosing a program and talked about my realistic chances of going into medical school with my stats through their program. Basically, with my very, very low uGPA (2.99) the likelihood of my getting into med school with anything short of a SMP was unlikely. With that said , I was on the extreme of low uGPA (average in a SMP tends to be like ~3.3).
I recommend you talk to the JHU people with your stats and ask them realistically how likely they think you can get into medical school with a good performance. Also ask them for what % of their class gets into medical school, and if you can squeeze it out of them also ask for the average uGPA of typical students that go there (this is key because if your uGPA is significantly lower than their average class, you will not be representiative of their class)