Congratulations! I tell people all the time that in most cases regarding Japanese vehicles, it is never truly cost effective to keep a new car less than 10 years. However, the many advancements that are bound to be included with your new purchase cannot be measured in dollars.
I our case, we are still very happy with our RX400h (also purchased in April of 2005). I am fairly certain, though that our next vehicle will be far lighter and more efficient - perhaps a Mazda 6 or Lexus ES300h. The consistent $4/gallon gas prices are the motivating factor.