demo? why are you installing a demo? the released version is out already...?
i remember playing the beta, they wanted to uninstall Sins as well...
what i recommend is backing up your save game files if you have any, then letting Impulse do whatever it wants to do. im not sure why, but i have a feeling Entrenchment uses alot of the same files that vanilla uses so they install them at the same time to make life easier, but dont quote me on that
the very worst that will happen is you will just have to reinstall vanilla manually and put your save games back in then contact Stardock support about it.
also, you definitly did not waste your $9
