Receiver downgrade?
I wouldn't pay money for the new receiver with LESS features.
Yes the new 1800 model has HDMI 1.3, but that is not required to receiver the new HD audio formats. All the current HD-DVD and BluRay players can decode the new audio formats and can output them via multichannel PCM to any HDMI 1.1 or higher receiver. You can take advantage of this on your current receiver and the new 1800 model wont have the upscalling feature of your current 2700. Spend your money on a new player or source material.
Check out a couple of the AH HDMI articles for more info.