I knew they had the cpu change planned some time in early 07, but since I knew of the heat issues, when I bought my 360, I bought a fan kit for it. It is a little loud and cost around $20 but well worth it for the time.
I highly doubt the new hd dvd drive will be included, but you never know, they may actually put in a faster or quieter drive.
HDMI port.. I don't need HDMI, as many companies speculate that hdcp? won't be implemented in HD DVDs until at least 2009, but you probably will get dvd upconversion and if you're lucky, Dolby TrueHD and other newer surround formats, which apparently you can't get through optical/coaxial digital output, only hdmi. The question is whether the usb cable on the hd dvd drive is able to carry that much audio and video data through it at one time.
The 360 also features 1080p over component, but not a lot of televisions support analog 1080p.
As far as a bigger hard drive goes, I think the 360 needs one a lot better. There are just too many games, videos, etc to store on the small hard drive, but luckily, you should be able to upgrade the hard drive (When one becomes available in stores) on the console you own now.