I had originally considered a dual Masters in Planning and Public Admin, but it would have cost me an extra two years going to classes part time in the evenings.
It might be fun to go back to school for a second Masters...I enjoy being around other students, sitting in lectures, discussing interesting topics, and learning new things. I would consider Law, Civil Engineering, or Public Admin for my own interests.
However, I don't miss having to work on projects during my liesure time. I don't miss spending a couple of nights a week on campus, away from my wife (and now my child). I don't miss having to pay tuition with an already tight budget. I don't miss having a long term committment to continuing a course of study that will invariably involve a course or two I really don't care about.
As long as I am able to make ends meet in my own field, using the education I already possess, I am unlikely to return to school before I retire.
If I were to go back sooner than that, it would be in order to completely change career paths... perhaps Agricultural Sciences with the accompanying purchase of some farmland...
Anyway, that's my take on the subject. It's fun to learn new things, but for me, the cost of an additional degree is way too high right now.