The resources folder in Service Studio should have drag and drop support like the images folder.
This way it should be possible to add multiple resources at a time or even complete folders.
Duplicate of: http://www.outsystems.com/ideas/750/manage-resource-folder
For the time being, you can use a command line switch to open Service Center to import resources by a folder of file mask. Not ideal, but fantastic if you have hundreds to do (like when updating CK Editor).