Matt2012,
Unfortunately, wrist injuries, and scaphoid injuries in particular, are very difficult to get over. It is not uncommon for patients to have a permanent decrease in wrist motion. The wrist does not take injury well, and tends to form quite a bit of scar tissue. The scar tissue prevents the patient from regaining full range of motion, especially hyperextension under weight.
The scaphoid is notorious for not healing well. While the vast majority do heal, there is a portion that go on to a nonunion. However, these are usually the ones that are displaced fractures. The "occult" and nondisplaced fractures almost always heal.
The problem is that the blood supply to the proximal pole is tenuous at best. The artery to the scaphoid comes in the distal pole and travels back into the proximal pole. Thus, when the scaphoid is fractured, this blood vessel can be disrupted. If this occurs, then the proximal pole can undergo AVN (avascular necrosis) and die.
But, again, this usually occurs in displaced scaphoid fractures, and what you had would be considered an "occult" scaphoid fracture. This are commonly not picked up on the first x-ray (and often not even on the 2 week repeat) and can sometimes only be seen on an MRI. But, the good thing, is that they usually heal okay.
But, that is just the bone. Remember, not just the bone is injured, but the soft tissues around the wrist are also injured, and it is the soft tissues that usually cause the problems with pain and decreased range of motion.
As to another MRI, you have to ask yourself what you are going to do with the information. If you are going to have a surgical procedure if it is not healed, then it is probably worth it. But, if you are just going to wait and see how things go, then it may not be.
Discuss it with your hand surgeon. But, you have found the common problem with wrist injures.
Good luck.