As I've said many times, I don't think any cruising grounds in Eastern Florida can compare to the wonderful St. Johns River!

First off, don't be discouraged by the river run to Palatka–wide, fairly featureless…it gets MUCH better the further you go beyond Palatka.
Silver Glen Springs and Blue Springs Parks are fascinating places— for your draft, anchor on the west side of Lake George and dinghy in to Silver Glen, water like champagne, a nice park, too.  At Blue
Springs, anchor in the river , avoid the manatee-only zones, dinghy ashore to the little "beachlet" and walk the boardwalks to see the manatees.  Pretty spot.
Our favorite anchorages  were among the Sisters Islands just south of the Amtrak railroad bridge–narrow and deep, use a trip line due to some log snags here and there;  also, in the mysteriously named "Hontoon Dead River", about a third of a mile around behind Hontoon State Park, anchor anywhere as there is no traffic.  Note that the docks at Hontoon State Park are outboard scale and depth–not for you!  Great dinghy exploring among the lillypads in the Hontoon, and the unusual black buzzards add to the otherworldliness of this place. Diesel usually available at Astoria and of course at the nice marina in Sanford.
Olrick

The Saint Johns is a very nice side-trip.  I second the comment that it's fun to go 47 miles up to "6 Mile Creek" where you can dock overnight free at The Outback Crabshack's very long dock on the
river.  Great food there too.  Then go further up past Palatka and take the winding jungle tour through Murphy Creek which is about a hundred yards wide but plenty deep to cruise.  Watch your charts and depth finder at the far end as it gets down to about 5 ft. where it rejoins the St. Johns.  There are very nice anchoraqges there completely off in the wilds and beautiful.
You can see what we did on our sidetrip there in our blog:
http://dougandkathysboatlog.blogspot.com/2007_03_01_archive.html  and scroll down from March 22nd through March 27th.
Have Fun,
Doug

Don't plan a short trip — plan a long trip!  Take at least a week,  go all the way to Lake Monroe and the nice town of Sanford, FL.  Use  Skipper Bob, Waterway Guide and Claiborne Young books to research the area.  Plan to anchor mostly — there are many, many lovely and protected anchorages.  Lots of birds, alligators and other wildlife.
I must urge you to stop at Six Mile Creek, about 15 miles upstream from Jacksonville, tie up at the free 1000 foot long floating dock and eat at the Outback Crab Shack.  It is a real experience.  You can
stay overnight for free if you buy a meal at the restaurant.  A  second highlight for us was the Welaka Maratime Museum in Welaka,  FL.  It is truly one-of-a-kind.  If you don't find it in the guides,
email me and I'll tell you how to find it.
You can see the highlights of our trip here: http://tinyurl.com/d2jpc4.  Look at days 342 through 351.
You will love this side trip once past Jacksonville.
Bill