I spent last weekend at Lake St. John. It was my first time there.
The lake is beautiful with lots of cypress trees and of course, there are plenty of docks and other structure to fish.
Although I had received several great fishing repots about St. John, the fishing really sucked last weekend. The wind was horrible...all day, every day. We didn't get to fish all that much bacause of the wind and when we did the fish just wouldn't bite.
Having said all that, it still was a fun trip even if the fish weren't biting much.
I do not know anything about Lake Concordia and places to stay there but we stayed at Neely's Spokane Resort right on Lake St. John. It's an older place mostly with four newer cabins to go along with the older ones and the people who run the place are really nice. Their website is at http://www.neelyspokaneresort.com/.
Hope this helps!