This tax and connector road is for 10,000 new homes in Watersound and another 100,000 north of the intracoastal. I'm guessing at the numbers from the amount of land St. Joe has for development. Watersound parkway across the intracoastal and all along HWY 79 in Bay County will add even more homes all the way up to I-10 and beyond.
Roads like these are how you make little old SoWal with all its supposedly protected lands open for development like everywhere else in Florida.
As for Seaside's money supporting the tax, I assume that is for their long desired plan to re-route 30A on the north side of the town, which will also have to be in the State Forest.