My first try:
When I started using extensions with Dreamweaver wan in “Ultra DEV” I found a couple of nice one, but when version MX came to be they did not install with the extension manager, and because this ones where free there were no update from the user. At that moment, had a client and needed some of those extensions to work. After been frustrated I decided to search where those extension where install on my UltraDev Ver and copy them to the MX Ver. To my surprise they work perfectly.
For this what I did was Copy the Configuration folder of the old Dreamweaver to the new. I started a Backup before any try, didn’t want to lose any application or reinstall it.
In the CS5.5 experiment whet I did was copy all copy the configuration folder from CS4 Ver in to CS5
The location is in windows 7:
For the Cs5.5:
C:\Users\[activeruser]\AppData\Roaming\Adobe\Dreamweaver CS5.5\en_US
For the CS4:
C:\Users\[activeruser]\AppData\Roaming\Adobe\Dreamweaver CS4\en_US
To my surprise every single extension for other companies started working perfectly.
From Webassit to DMXZone worked without problems, now the ADDT started working like 25% of the features.
Other just tells me there are missing files and have to reinstall the extension. I’m looking for those missing files. 
So if anybody what to give it a try, back up your original configuration folders for each application and try it, if you find anything else post it, maybe we can find a workaround the dilemma of not having an update of the extensions we love.