While I'm not expert on either, I do own the WT-1.
The main differences between the two is that the WT-1A uses 802.11b while the WT-2A uses 802.11g which is faster. The WT-2A also allows you to transfer just the JPG image which is considerably smaller than NEF files.
They are basically used for studio work where you can shoot untethered and have the image show up on a monitor for review.
A good friend of mine has both, I've been testing with both on his D2H and D2X. The WT2 is NOT faster that 11mBIT in AD-HOC mode (which you probably want to use anyhow)!!! I've tried pretty much every trick in the book but doesn't get faster than this.
You can set the camera to only transmit JPG files to view on a notebook or large studio beamer for review of the shots, pretty impressive and it works fairly well, takes about 4-5 secs to transmit a single JPG file.