Yes, Fort Wilderness is worth it. Having said that, the "free meal plan" which is sometimes included with staying in other on-site Disney hotels can save a lot of money. But... The Fort is an awesome campground just by itself!
Too bad you only have 4 days there, you will find it is just not enough time.
"Hoop-de-do-Review" at Fort Wilderness is worth seeing.
There is so much to do there, really consider if you want to wait in line for a ride for 2 or more hours. Take advantage of whatever they have for the "fast pass" system these days, use that for the most popular rides. Otherwise, look around! There are so many attractions, shows, rides, etc there might be something right behind you that has a short line and is very much worth seeing.
Keep your eyes and ears open for specials, passes, etc. Sometimes employees walk around giving out "stay late" passes or "get in early" passes... they can really be fun to use.
Does someone in your group have a special occasion? anniversary, birthday, etc? Get a button from the town hall to wear for that occasion. Employees will see that and it is fun getting recognized, and sometimes (many times!) they will do something special for the person or group - from an extra dessert or treat to maybe giving you a special access pass of some sort.
It has been almost 10 years since we've been, so I am sure some things have changed.
Look around on forums for ideas and tips, and when you are at Disney... Ask! Whatever the question is, many times they will go out of their way to help.