Tulane is a pretty sweet deal if you want to go to Tulane, and I don't know much about GEMS.
Before deciding which to pursue, it would be prudent to figure out if your application could really benefit from one of these programs. If you have a sub-par GPA or a less-than-stellar MCAT then one of these might be a good idea but there are other instances in which you could save time and money by skipping the SMP and just focus on reapplying.
An example: you applied late so you only received a couple of interviews and one waitlist, even though your app is otherwise competitive. Solution: reapply early and save the thousands of dollars it takes to attend a SMP, as well as avoiding the risk of causing harm to an otherwise strong app.
Good luck with your decision.