Just a few more thoughts on this subject...
If you have a good electric guitar with good pickups, you already have a pretty unique and harmonically rich signal coming out of the guitar. Now you need an amp that won't interfere with that too much and will only add good coloration.
Most classic tube amp designs do just that.
To my mind, a graphic EQ is more suited to bass or setting a permanent EQ for a sound system in a room (where you want to adjust certain frequencies to balance out the peculiar "room sound"). I guess it's also useful for recording, when you're trying to get each instrument to fit into its "frequency shelf" so you can produce a clear, loud, realistic mix. (For example, rolling off 100 hz on guitar tracks so you hear seperation between the 6-string and 4-string)
For playing live, I don't see the need for a graphic EQ, but that's just me. Rather than say, "I'd like my 5k dropped by about 2 decibels", I might just turn the treble down a little (5k is treble, right? )