There actually was a lot of data gained about hurricanes that we did not have before during Stormfury -- consider it a secondary benefit of the project.

The seeding and planned weakening aspect of the program, the primary objective, was a complete failure. And...seeding, if it worked, could change a storm's path. Making a storm weaker makes it susceptible to different steering currents; it's not likely that a substantial change would be realized unless the angle of approach were something like Charley or any of the recurving East coast storms, but changing something from New Orleans to Pensacola is certainly feasible. Making a storm shallower well out to sea could keep it moving west longer, making it a greater threat to land. Just yet another thing that must be taken into consideration...and why you'll likely never see any modification program taken seriously (especially Dynagel and it's 4000 variants).