It really just depends on how much dynamic range you want to preserve. Sometimes, the dynamic range is so broad, it makes listening difficult on all but a high end playback system. Personally, I find it a bit overboard to bring quiet, acoustic songs up to the same level as loud, electric songs. Boojum's approach will work nicely, and allow you to set levels for each track. I do sometimes apply compression or amplify to bring very quiet tracks to a higher level for easier listening...just not all the way up to the level of the loudest tracks. Really, it's up to your personal preference. Just make sure you maintain an archive copy of the original source, with full dynamic range, so if you wish to modify later, you're able to do so from the original.