Ok. Your proposal and effort were fair, I will give you that.
Regarding the S51, I don't reside in S.I. so I wouldn't have any first hand experience with the route.
I can only assume that it's proably used as a feeder from St. George to South Beach. Additionally, Midland Beach folks may use it as a feeder to SIR & Hylan, especially now that the S79 was implemented. Of course I could be way off, but it doesn't look like many people are riding point to point on the route.
Not to put you on the spot, but Checkmate, could you perhaps elaborate on the route, please.