As far as synthetic oil goes, I really do not think this is necessary, nor will it substantially lengthen the life of your engine. I would also point out that most of the time you will trade your vehicle in long before you would really see any gains from synthetic oil in terms of longetivity.
Having said all of this, if you are committed to using a synthetic, then I would do it, but would follow the change interval for "normal use". I think it is a waste of money, however. Conventional oils are much, much better than the oils of even a few years ago.