Woodruff is a pretty decent crappie lake. Its fairly shallow and when people are fishing in the middle they are most likely fishing a weedbed for some kind of structure in the middle. I'd say go to those areas and try next time. Should be getting close to prespawn there now so theres gonna be some nice fishing there soon. There is a good guide on the lake with a fishcamp. I don't remember the name, but you wouldn't hurt yourself giving him a visit. He's easy to find.
I actually lived on the St. Johns river for a winter, and got some real nice crappie there, but like you I never really hammered them. I found the numbers to be similar to bass fishing, but real nice sized fish. I never caught more that 15- 20/day.
There are some very intersting fish in the St. Johns. The water from the springs comes out of the ground at a constant 72 degrees all winter, so around the major springs some fairly unusual fish show up. Saltwater fish come into the river that far and I've seen tarpon, redish, snook, and some I don't know what they were. Some kind of pufferfish or something way down in the deepest part of the deep pools near the springs. Keep an eye out for manitees. I saw them many times while fishing the river.
I lived in DeLand right next to Woodruff and the St. Johns. If you want to go somewhere interesting to fish - go to the Woodruff Wildlife preserve and fish the canals. They are full of bass, gar, panfish, and alligators - Big ones. There is one that suns himself on the back left corner of the preserve thats 14 feet long. I've been within about 50 feet of him. He's impressive. The birds there this time of year are awsome. Be there at sunset and you'll see something that will amaze you. I won't ruin it by telling. Also, go see the manitees at Blue Springs State Park.