The 06 has 316L stainless steel jet trim and the valve for the waterfall and for the neck Atlas system need only a 180 degree turn, rather than having to turn them a whole bunch of time to go from off to full power. Also there are a couple of color changes. That's pretty much it.
I concur. These are welcome changes, but not Earth shattering. If you can get the '05 sooner, go for it.
Sorry I didn't see this sooner -
Caldera
is Watkins Manufacturing, the people who bring you HotSpring, Tiger River, Solana and Hot Spot spas. You can bet your wife that they WANT to talk to customers - they spend a fortune on advertising, brochures, web sites and the like. The way they like to accomplish the actual conversation is through a good local dealer. They put a lot of stock in that relationship.
As to the changes - for the first time in the 20 years I have dealt Watkins, they are forecasting no price changes. Certain costs may gang up on the local dealer to require a price increase, but the cost of the tubs this year should remain almost level from last year. Those other costs are things such as:
Increased rent
Increased fuel prices which affects shipping
Increased power costs
Increased college tuition...
YMMV