In case it hasn't been mentioned already: You can open all of your Garageband projects in Logic. You'll have access to all the same effects, loops and channels that you had in GB, but you'll be able to continue adding to the project without having to rebuild anything.
Interestingly, sometimes I like to write something in GB so I don't get overwhelmed with "option paralysis", then open the project in Logic when I am ready to do so. A change of scenery isn't necessarily a bad thing at times!