I use AE myself. Motion has some useful built-in particle effects, but does not have the complexity of AE, so I never use it any more. Give yourself time with AE, as it has a big learning curve. I recommend following many of the great online tutorials, like on AETuts+, as creating complex effects will help you better understand the program's deep functionality.
So yes, get it, if you have a use for it. Right out of the box (without 3rd-party plug-ins) it's an excellent matte and compositing tool.