I have thought about this one too...I guess since eCart is a newer update maybe update that last.
but what I plan to do is the following:
1. delete the Configuration folder
2. open up adobe extensions manager and then uninstall all the "redunant" webassist products.
3. load up dreamweaver which will create a new configuration folder
4. load up adobe extensions manager and install in this order (if i had design extender)
a) install design extender
b) install databridge
c) install ecart (latest build)
but then i could be wrong with installing ecart last.