Two years ago we left Miami Everglades RV Park just off Krome Ave (997) and took that up to US27 and then on to Sebring. You'll definitely miss Miami this route. I was also interested in seeing what it looked like up along 27 and found that there isn't much other than cane farms. It was still interesting to me because I enjoy different landscapes. There wasn't much traffic along 27.
We stayed at Long Point campground, a Brevard County park just north of Sebastian Inlet, last year. Would have opted for the state park, but waited too long. There's a nice little museum south of the state park that's all about Spanish ships that sunk with great treasures centuries ago. I believe it's state operated. We enjoyed the visit, very interesting.
Our trip to Long Point was from the Arcadia area, but we took 70 to Okeechobee and then stayed on 70 up to I-95, then north to the Vero Beach exit. You could always take 27 up to Moore Haven and then 78 up to Okeechobee and 70 east to I-95. Not sure what 78 is like, but 70 was ok for us.
I will again mention that it's not a real exciting route, but you stay off I-95, get to see the levee around Lake Okeechobee, and you won't find a flatter route anywhere. :D