If you have the expansions, the journal becomes *much* easier to use, and you can annotate your map.
Also, most of the really good player made plug-ins, require both expansions. The plug-ins add many additional hours of play: large and small quests, companions, new textures, houses for the PC, new wildlife etc. They can even make the game more challenging.There are thousands available.
Check out the mod sticky at the top of the page for more info.
Oh, and the expansions themselves add a lot of really great content as well.

I especially like the quests and graphics in
Bloodmoon.
Tribunal is fun too.
All in all, the GOTY Edition is a really awesome deal!