Yes, there are people that can afford insurance, yet don't purchase it. These people still won't purchase insurance until they are sick, but will simply pay the fine - since it's smaller then the premiums.
However, if they do actually purchase the insurance, it won't cause the nation's health care spending (as a whole) to decrease. By having insurance, they are more likely to go to the doctor for minor things (cough, scrape) and will still have to go to the doctor for the big things (MI, CVA, etc).
I've also seen studies that show increased preventitive maintenance (something your friends will now obtain free) actually causes increased national spending on healthcare. The reason put forth was that you can't tell who would have been affected by the disease being prevented, so you have to provide it to everyone. Everyone receiving the preventative care is a larger cost, overall, then caring for the relatively small percentage that will actually contract the disease/condition.
What increasing insurance coverage to more people will do is more evenly spread the greater costs to everyone that has insurance or pays their bills without insurance. Again, it won't actually reduce the nation's overall spending on healthcare.