Not unless you really need the elements of VISTA in your install. Otherwise, WXPP is a much better choice.
The upgrade limits you significantly when/if trouble comes later on. You lose the ability to run various repair functions.
VISTA upgrades have so far been substantially more trouble than other versions. If you want to make a wise choice, spend the extra mony for VISTA premium, but I remain convinced that WXPP is a much better choice.
Later on, sometime between November of 2007 and March of 2008, Microsoft will issue the Service Pack 1 Version. That will be the time to decide...
But even with SP1, I would not get an Upgrade version... because it is crippled in too many ways when fixes are necessary.