Definately keep your discs... if there is anyway to prove you purchased your library legally having those discs is a sure fire way... and as you stated if the computer goes tits up you have a backup contigency in place already to go.
BIN files are basically the same thing as the CDG except that CDG is more widely accepted for playback... think of the BIN file as a Binary representation of the Data file you ripped with the audio.... a CDG is basically a CD Graphics file... BIN files also tend to be larger in size.
My advice to you however instead of using Audiograbber to rip your karaoke checkout Power CDG Burner instead you'll get near perfect if not perfect .cdg files... http://www.powerkaraoke.com/src/prod_powercdgburner.php
Useing that program to rip my karaoke files I get graphic files that are clean and have no graphicall errors in them... I mean when you playback these no one will even be able to tell if you are using disc or mp3+g files it's that good.
And here's the best part... almost any CD-R drive will work...
EAC and Audiograbber are great at ripping mp3's but Power CDG Burner is, hands down, THE BEST at ripping karaoke. BTW it's great at burning back to CD-R as well.
