I have done 1 track day so far and agree it is a great way to improve your riding skills. Plans for more in 2016.
I have also taken the Stayin Safe program lead by Eric Trow and found it to be a great way to get professional coaching while riding on the street. It is a 2 day program that is held on the street in various location around the US. I took it in West Virgina. You spend 2 days riding great roads and get interactive coaching via headsets which provides instantaneous feedback in real world conditions. It focuses on both street awareness as well as bike position and body position. Small student to instructor ratio is key - we had 4 students and 1 instructor. For me, the 2 days was the most effective motorcycle training I have had.