If you have a working system, and don't need the newer features, it's probably not a bad idea to stick with what is working until you need something new (it's a bit like upgrading operating systems -- you do it when you have to).
The fuerte->groovy->hydro upgrade path is unfortunately a bit rocky given the transition from rosbuild to catkin. Fuerte was primarily rosbuild, with a few experimental catkin packages. The version of catkin in Fuerte is quite different from later ones. And, as is true with pretty much every ROS update, the API of the Point Cloud Library has changed (quite significantly in Hydro as PCL removed all ROS messages from their internal code, but the new pcl_conversions package does help with code transition)
Groovy is at this point quite stable, with any new developments (and associated bugs/regressions) pretty much being done now only in Hydro. Groovy is still is a mix of rosbuild and catkin, with some major pieces (such as navigation) not being catkinized, which can be a headache if you're actually looking to make a single quick transition to catkin.
Eventually, you will likely want to upgrade to using catkin when you move to or past Hydro. With Hydro, all released packages (those you get through apt-get) are using catkin. Most of them are also now a bit more tested given the longer Hydro beta cycle, so errors introduced during catkin updates are likely to have now been caught.
A good reference is the release/migration pages, which will give an idea of the MAJOR changes in released packages for each release: