I sprung for the X2 -> X3 Upgrade last night. Downloaded and Installed X3A. Have yet to install the X3B patch -- will do that tonight.
 
I already have Dimesion Pro 1.5 installed from x2. Should I install it again (is there any difference in the download that was part of the X3 upgrade)?
 
Also, should I install the X3B patch before installing the Loops & One Shots, Dimsion Pro 1.5, Dimension Pro 1.5 Expansion Packs, and Addictive Drums? ... or does it matter?
 
- the bbdude

No need to install (or even download) Dimension Pro, or its expansion packs, nor the loops and one shots, if you already did those during an X2 install. All the new content is available from the standard X3 install (such as Melodyne Essential, BlueTubes etc.) with the exception of Addictive Drums which uses XLN's own installer, available at their site (you get the key in your Cakewalk Store Account).