The key is to be able to increase average levels without squashing the material; it doesn't have to be one extreme (absolutely no processing) or the other (brickwall limit the audio).
The volume knob thing can be a real drag if you're also transferring your digitized LPs to your iTunes library and listening to it in shuffle mode.
If anyone's curious, here's a "gently-boosted" track off my Guitar Forms album by Kenny Burrell (audio drop-outs done on purpose):
01 Downstairs.mp3