Some take a "if it ain't broke, don't fix it" attitude to driver updates, which makes sense, but display drivers might be a exception since they tend to add performance optimizations. I generally try to keep my display driver up to date. Usually newer games won't run on older drivers (and sometimes old games won't run on newer ones). Example: ATI has been significantly improveing their anti-aliasing performance over the last few years.
nVidia don't release their drivers for different products separately but have them all in their ForceWare package. Here
is the list of the products supported in the latest ForceWare package.
Both ATI and nVidia list the changes in their release notes, where you can see if anything which might be important to you has been updated.
nVidia's lates is ForceWare 91.31
ATI's latest is Catalyst 6.7