Chris, I use trackdays now for plain old fun, and as a way to improve my racing. When racing, I basically use "what I got". There isn't much opportunity to work on improving my riding. It is GO time! I use the tools I already have and use them to their limits. Trackdays are the time to get new tools, or refine existing tools.
Racing and trackdays will always be a part of my activities, but I have different mind sets for each. Trackdays are for good times with friends, and helping others - and a little bit of friendly competition. Racing is still for good times with friends, but there is a much more competitive, serious aspect to all of it. A killer instinct.
There is a good amount of pressure I place on myself to race well. That level of pressure doesn't exist for me in trackdays.
But I do agree with Todd and Katie on this one. It does change your outlook. The question is really a personal question about what motivates you to ride. Competition, improvement, fun, all the above?