Its important to have a guitar you like the feel of, as you'll play more naturally with it. But without a good amp, you're basically pointing a good remote at a broken tv. Pickups matter a bit, and speakers matter more potentially. The part where it stops being scientific at all comes in with adding it all together; certain amps sound better with certain speakers, certain amps sound better with single coils or humbuckers....... It's a wonder anyone has time to write songs. I think we find a sound that speaks to us and run with it.