If you go thru one time and adjust the overall volume, it will likely be worth it.
If these are stereo files (not multitrack) then the edit-gain change' has a normalize preset that brings everything up to a certain set point. It just adds volume until the loudest part of the file is -0.3 or so.

Run each song thru that, using the hard write method, make sure all sliders in use are all the way up for each one and render away. Using the effect from the edit pulldown with the whole song hilighted (so it processes the whole thing) will hard write the change, then using 'merge audio to stereo wave file' (or compressed file if wanting mp3) in the Audio pulldown will write it to disk again. Save As another name if ya want to keep the originals.

I do not work here, but the benefits are still awesome
Make your sound your own!