These diagnostic tests may detect Parkinson's earlier than symptoms appear. If we were to find therapies who could slow Parkinson's or preserve dopamine-producing brain cells, we may be able to provide people with more symptom free years. Furthermore, there are a few people who have been diagnosed with Parkinson's disease when they actually have a different Parkinsonism or other condition. A more precise diagnosis could mean more ideal treatments.
All these tests are still in the experimental phase. However, in a disease without a definite way to diagnose it, we could all of a sudden have three choices. We suspect the blood tests will beat out the more expensive SPECT scan, but you never can predict such events.