I noticed that after the 507, you are heading right for Elephant Lake Rd via Loop Rd. I added in Glamorgan Rd #3 and Essonville Line #4, which adds just a few minutes, but is much more fun. Between those two, you also get to ride along one of the most scenic sections of the 118 (beside Loon Lake) which is very nice.
Taking the slab all the way from Huntsville can be mindnumbing. After going through the park take the 35 south from Dwight. The 35 down past Dorset and on to Minden is a very nice scenic ride with excellent pavement and fast sweepers. In Dorset there is a lookout tower that has really far reaching views of the area. You can then drop down and ride past the Kirkfield Locks and causeway along Centennial Rd - very scenic.
Overall the changes add just over an hour to your ride but should make it quite a bit better.
http://goo.gl/maps/6qWaE